A New Hope/WMG

Obi-Wan's Force Ghost mind-controlled Tarkin not to send the TIE fighters out.
Tarkin may have been proud of the Death Star, but he was no idiot. Even he would have seen that turbolasers are hard to aim, imprecise, and generally Cool but Stupid. TIE fighters would have made sense even to him. Obi-Wan was the culprit for his erratic behavior. He used a Mind Trick to get him to hold back the fighters.
 * They did deploy the TIE fighters as soon as they realized that it was simply small manned fighters taking the Death Star.
 * But by then, Obi-Wan was busy helping Luke aim the torpedo, and was distracted. And, technically, only Vader's squadron attacked the Rebels.

Obi-Wan killed Uncle Owen and Aunt Beru.
Obi Wan killed Owen and Beru Lars so Luke would go on the heroic journey with him and the droids. Nobody seems to pick up on this, He blew their house up while Luke was out searching for R2. He had been planning it for years.
 * That would imply-Ben is on the dark side? That would make sense. Obi-Wan on the Dark Side would explain that, and why he dragged Luke to Dagobah when he could do more good with the Rebels.

Vader didn't want to kill Obi-Wan.
He seems kind of reluctant, stating that he "should not have come back". After spending years with the empire, Vader deeply regrets what he has done, and really didn't want to finish Obi-Wan of till he actually asked him to do it. Vader could have tracked him down soon, as he was aware of his presence, and killed him off soon. Instead, he duels him like a worthy and respected opponent.
 * The duel was as much a meeting between a former master and apprentice as it was an actual fight to the death. Vader's "now I am the master" comment is dismissive of Obi-Wan's skills and praises his own, he wasn't unleashing all of his power on Obi-Wan because of any respect he had for him, it was because he had a few choice words for his old master. If you keep it original trilogy, look at Vader fighting Obi-Wan versus him fighting Luke in TESB, this of course does not get into the ultra-Vader we see in the EU. Vader pretty readily strikes down Obi-Wan when he is offered the chance to make a death blow too.

Grand Moff Tarkin was a rebel agent or sympathizer the entire time.
The destruction of Alderaan was a ploy to ensure the collapse of the Empire by creating dissent.
 * Tarkin intentionally lost the Battle of Yavin.
 * Tarkin deployed less than a dozen Tie Fighters against the Rebel strike force, a fraction of the station's forces.
 * It was actually more than that, and note that out of thirty attacking Rebel fighters, exactly three of them are alive ten minutes after the Imperial fighter counterattack begins... an anonymous Y-wing that apparently hung back from all the action, an X-wing piloted by the single best non-Jedi starfighter pilot to ever live, and an X-wing piloted by Luke Freakin' Skywalker. Releasing sufficient force to overwhelmingly wipe out the attacking enemy, to the point where the only survivors are two nigh-unkillable fighter aces and a shirker, is by no stretch of the imagination 'intentionally holding back'. The only reason the Rebellion won the Battle of Yavin is because the single most powerful Force-Sensitive then alive in the galaxy was there. Oh, and Han Solo, who is the greatest non-Jedi pilot of anything.
 * According to the EU Death Star Technical Companion, no. The Death Star carried 7200 TIE Fighters and over 20,000 other combat space fighters. Wedge Antilles himself answers the question in the Companion. Tarkin never ordered any fighters to engage, believing that the turbolaser batteries would be enough to repel the rebels. It was Darth Vader's personal squadron that went out and met them. According to Wedge, "We may have still won the day if all of the TIEs had taken to space, but it sure would have been a lot more crowded over the Death Star." BUT, it's still up to debate and well within this WMG as to whether or not Tarkin held back launching an all-out counterstrike out of typical Imperial arrogance or whether he wanted them to win...
 * Launching 7200 interceptors vs. 30 enemy aircraft does nothing except vastly increase your risks of suffering mid-air collisions. Its folly on the same level as engaging an enemy platoon with an entire division... most of your units won't even have a clear shot, due to the other friendly units in front of them. The Rebel casualty figures and how rapidly they mounted up would indicate that Tarkin released a sufficient amount of forces to quickly defeat the Rebel fighter attack. Unfortunately, one of the few Rebel survivors was a psychic superhero capable of single-handedly destroying the Death Star.
 * Tarkin leaked the Death Star plans to the Rebellion.
 * Alternatively, Tarkin wasn't an agent or a sympathizer; neither would have killed billions of people with as much readiness as he did. Admiral Ozzel (Vader's first victim in The Empire Strikes Back), on the other hand, was rather bumbling for someone of such high rank in The Empire, due to actually being a Rebel agent. He attempted to draw Vader away from the readings from Hoth (despite probably seeing first hand what Vader does to those that disagree with him), and when that failed, he ordered the fleet to come out of lightspeed too close to the system, sacrificing his life in order to give his comrades the chance to escape.
 * The bit about Ozzel being a sympathizer is similar to a humorous sequence in one of the X-Wing EU novels, only it's about Captain Needa, who loses the Falcon later in the movie. The commander of a really backwater imperial outpost is a relative of Needa's, and is instructed by his men to tell the story to the New Republic when they show up to capture the post, so they can keep their jobs.
 * His absence at Yavin's victory party argues strongly against this. Because in that timeline, it would have gone "Evacuate? In our moment of triumph? Well, OK just to be on the safe side..." Remember, Tarkin had a chance to escape the Death Star's destruction that he chose not to take.
 * Why would he go to the Rebel victory party on Yavin? That'd have blown his cover. Vader survived, and so did other guys. Ozzel was deep cover, and managed to survive long enough to give the Rebels a hand at Hoth. He died doing so, but that means he was able to remain in high up in the Imperial Navy and covertly give the Rebels a little help here and there at crucial moments. He might not have even been a "plant" of the Rebels, or have ever met with any of the leaders of the Rebellion; he could have simply been an Imperial who came to sympathize with the cause of the enemy and decided to use his position to aid their cause.
 * If Tarkin's plan was to destroy a major planet to bolster the rebellion against the Empire, he had to die with the Death Star. He would be killed by the Emperor for failure or by the rebels for blowing up a planet.
 * And what exactly would stop him from leaving the Death Star right before its destruction and then quietly retiring on any one of a million planets in the universe? Its not like the Death Star's destruction left behind an identifiable corpse...
 * If he was a rebel sympathizer/spy, then the reason he stayed on the Death Star is obviously out of guilt for having having destroyed Alderaan, realizing that he had gone way over the Moral Event Horizon.
 * For that matter, if Tarkin wanted to blow up the Death Star, he simply had to go to an engineering console, boot up his superuser access account, and deliberately trash the failsafes on the main reactor controls. And then hop the nearest shuttle out of town before the timer ran out. When you're the guy in charge, sabotage becomes a bit easier.
 * Even if he didn't have the technical skills to do this himself, nothing could stop him from just walking a Rebel-programmed R2 droid to his personal command console -- or the central reactor controls -- and telling it to have fun. "Sir, what are you doing?" "Having this droid do a personal audit of system status for me. Now go away." "...yes sir."
 * Tarkin could not engage in any overt acts of sabotage with Vader watching over him.
 * Vader wasn't on the Death Star until the same day that its construction was finally finished. Tarkin had all the time in the world to set it up.
 * Of course, one possibility is that he had several plans working to sabotage the Death Star -- all of which would've been more subtle than the above -- and the whole get-Rebels-to-blow-it-up thing is simply the one that worked first.
 * Whole WMG Jossed big-time by Death Star, which gives us a peek inside Tarkin's head. He loves the Death Star (indeed, his portrayal in the novel occasionally veers into Cargo Ship territory). He turns into a barely-controlled ball of fury whenever someone scratches the paintwork and enters the kind of thought patterns that include the phrase "How dare they" at least every other sentence. His failure at Yavin was partially due to the main gunner's tortured conscience causing him to delay firing as long as possible, partially due to not actually knowing the exhaust port was a viable target, and partially due to his Tarkin Doctrine being a philosophy based primarily on a failure to understand how the Rebels think.
 * Michael Reaves and Steve Perry are concealing Tarkin’s motives by collaborating in Death Star’s publication.
 * Michael Reaves and Steve Perry are working for Tarkin, who survived.
 * Steve Perry is Grand Moff Tarkin, who co-wrote the Death Star novel as a cover up.

Tarkin destroyed the Death Star
Following on from the above theory about Tarkin being a Rebel sympathiser. Tarkin had worked out how to sabotage the Death Star long before it was completed, and wanted to do so before it destroyed Alderaan. However, the Rebel Alliance needed a great symbolic victory, so they insisted that the Death Star should be taken out in an attack by Rebel forces. This also allowed room for the other great rallying symbol, the destruction of Alderaan. Tarkin didn't like it, but he had to accept the propaganda value. So he helped the Alliance leadership cook up some bogus schematics showing off a 'key vulnerability' which didn't exist - the Empire's engineers just aren't that dumb. Then he timed the destruction of the Death Star to coincide with the attack. The Alliance wasn't planning on any pilots coming back from what was, effectively, a suicide mission; after the explosion they'd just claim one of their fighters must have got through against the odds.
 * Thanks to the novel Death Star...no. Spectacular no. His initial reaction (and final reaction) to being told that the Death Star was about to explode is a two-second Villainous Breakdown with the mental Madness Mantra "Inconceivable". (And in this case, it does mean what he thinks it means - Tarkin is literally unable to conceive of his idiot doctrine being wrong or his beloved station being destroyed).
 * That’s what Tarkin wants you to think, just a planned.
 * According to Word of George the EU is an expanded "alternate universe". clearly Alternate!Tarkin has the opposite views and personality from Movie!Tarkin, and it's just a mirror universe forced coincidence they end up acting mostly the same way.

Tarkin lives!
"Evacuate? In our moment of triumph? I think you overestimate their chances." "Yeah, you're right, sir. Sir? Sir?"
 * He's probably on some resort world somewhere, sipping margaritas and attended to by nubile women.
 * And he has an unlisted Com-code, to get away from Daala.
 * He's due to star in fanfiction any day now.
 * His escape pod got caught in the blast, and he's now an amnesiac searching for his identity in The Tarkin Identity
 * He's made a new living as a Courscanti rapper, Tar-Pac!
 * Considering that as far as this troper recalls Tarkin was giving the firing countdown right before the big boom, he's almost certainly space dust.
 * He left a clone or a hologram behind to cover his escape.
 * Actually, he was blasted through a space/time wormhole and ended up on Earth sometime in the 19th century. Once there, he decided to resurrect the Tarkin Doctrine, but using a new weapon of terror: a homicidal, artificially-created man.

Captain Antilles was an Imperial agent or sympathizer the entire time.
''That's funny. The damage doesn't look as bad from out here''. No, and you know why? Antilles shut off the engines himself after some frankly half-hearted blaster exchanges between the Tantive IV and the star destroyer. Didn't go quite as planned for him though when Vader took the "don't blow Antilles' cover" instruction a tad too far.
 * But Captain Antilles was right there in Revenge of the Sith, witnessing Bail, Obi-Wan, and Yoda sow the seeds for the original trilogy. If he were an Imperial spy, the Empire would know where Obi-Wan and Yoda went into hiding and what happened to Anakin's offspring, among other things.
 * Captain Antilles is Chaotic Evil.
 * He shut down the engines and let his ship be boarded because he's not an idiot and knew that taking on an Imperial Star Destroyer would be suicide. He only wanted to give Leia enough time to smuggle out the Death Star plans, and his plan worked.
 * That's what Captain Antilles wants you to think!

The Obi-wan that trained Luke is a ridiculously human force-made android made by the real one.
An idea from the Robot Names page. When the Skywalker twins had to be separated, Obi-wan knew he needed to protect both of them. He used the Force to hastily put together an android he named OB-1. However, because he figured Luke wouldn't become necessary for several years, he made the force-android several decades older. Obi-wan followed Leia to Alderaan (since she was going to be the high profile bait) and OB-1 went with Luke. Several years down the line (but not enough for the aged OB-1 to be accurate), Leia gets captured. She hurriedly composes a message to Obi-wan on Alderaan and sends it to the nearest planet Tatooine hoping it will eventually get to Alderaan. R2-D2 ends up with Luke and is taken to OB-1 by mistake. OB-1 isn't lying when he says he's never owned a droid and that Darth Vader killed Luke's father because that's what Obi-wan told him happened. OB-1 decides to train Luke and bring him to Obi-wan, who ends up dying when Alderaan explodes. Later when Darth Vader strikes OB-1, he just vanishes because Obi-wan isn't around to will him together. The force ghost of Obi-wan never tells Luke this because frankly the kid has enough problems to deal without without knowing his mentor was really a some sort of construct.

Obi-Wan planned to die at Vader's blade
Well, not in the sense of talking with Vader about killing him beforehand, but being a Jedi, he should have known that a blade was coming right him, yet he just stood there and smiled. He knew Vader was waiting to see Obi-wan for several years and decided to let himself get killed by Darth Vader in a brief Xanatos Gambit with the direct intention of motivating Luke to join the Rebellion and become a Jedi.
 * This is not canon? He lifts his saber out of the way and everything...
 * He DID tell Vader he'll "become more powerful than [he] can possible imagine" if he killed him.
 * He also saw Luke, Han, and Leia, all by the Falcon. A legion of distracted storm troopers were watching him and Vader. He had the tractor beam disabled (he didn't know that it was all a trap anyway, but still). He also knew about how to become a Force Ghost, a far more useful ally for Luke than a crusty old body. He also knew that L Uke wouldn't leave without him if there was a chance of saving him. Throwing the fight was the optimal choice.

Obi-Wan threw the fight just to infuriate Darth Vader
It's something Vader was really looking forward to, what with the dramatic 'we meet again' speech. And what happens? Obi-Wan just lets him win. No grand climactic fight, no revenge for his defeat twenty years ago, no closure. What could be more infuriating?
 * Heck, it might be even more infuriating than just beating or killing him.
 * And beyond just tweaking Darth Vader, it may have been planned to throw Vader off his game. Just As Planned

Obi-Wan let Vader win to save Luke from Vader.
Obi-Wan originally planned to sneak back to the others without confronting Vader, but Vader intercepted him in the Death Star corridors. His priority then became to distract Vader long enough for the others to return to the Falcon and take off before Vader could sense Luke's presence in the Force (which presumably is already more noticeable than Leia's) - he knew Vader outclassed him in fighting power, but was stalling for time. When the storm trooper guards move to watch the fight the other heroes run to the Falcon, but Luke notices the duel taking place. Obi-Wan knows that Luke is seconds away from shaking off his shock and running to help, which may or may not get him shot by storm troopers but will certainly get him noticed by Vader. He has only one option that will both remove Luke's reason to stay AND shock Vader into distracted surprise for a few more seconds, and that is to allow Vader to strike a killing blow. When Luke STILL doesn't move, Obi-Wan's spirit has to reach out through the Force and command him to run.

Obi-Wan Kenobi and Uncle Owen were clones.
The names Obi-Wan (OB-1) and Owen (O-1) sound suspiciously like serial numbers. Therefore it's possible that they could be two clones produced during the Clone Wars. Obi-Wan may have been either a clone of a Jedi, or just a clone who became a Jedi.
 * Needless to say, this theory has been Jossed into oblivion since The Phantom Menace. But it was reasonably popular once upon a time, and it's worth mentioning.
 * Who says that the Obi-Wan in IV is the same one that's in III? The old Obi-Wan died, but they cloned him to carry on the fight. Ditto for Owen.
 * Hell, the real Obi-Wan may still be out there.
 * The OB-1 and O-1 in Episode IV were subjected to accelerated growing, thus explaining why they appear to be 30 or 40 years older, rather than only 20.

Obi-Wan Kenobi attempted to craft the perfect assassin out of Luke.
In his time of isolation Obi-Wan became warped and slightly insane. As a result his warped mind lead him to plan a path out for Luke that would result in him killing Vader. The first obstacle was getting Luke to let go of his life on Tatooine. This was accomplished by sending an anonymous tip to the imperial stormtroopers of the location of the jawa's who sold the droids to Uncle Owen and Aunt Beru. This cut Luke's ties on Tatooine and solidified his hatred of the empire. Before this he lied to him telling him that Darth Vader killed his father, cementing a hatred for Vader to prevent Luke from opting out of Patricide. The next step of his plan is to train Luke in the force and lightsaber. He knew that at some point he would run afoul of Vader and had a plan for that as well. Lead Vader to fight near where the Falcon was docked so that Luke would see the battle once he and the rest of the party arrived. He then smugly let himself die becoming more powerful than Vader could ever imagine, by empowering Luke the son Vader did not know still lived.

Han never believed in the Force, he always thought the Jedi were full of crap
All of them getting killed didn't help.
 * This is canon. Han would have been maybe five at the most when the Jedi were massacred, most people would never meet one (There were only a few thousand Jedi at any one time) and the Empire made a concerted effort to convince everyone that the Jedi never had any real powers. Han does believe this, so does most of the Galaxy.
 * Alternatively, Han worshipped Obi-Wan Kenobi and Anakin Skywalker as a kid. They were known war heroes (as pointed out in the novelization of RoTS), and Han wished he could be a Jedi like them. After several Jedi were killed, Han's parents told him not to say even word about them in fear of Vader/Palpatine finding out someone still aligned with the Jedi. Han felt betrayed by the Jedi, and started hating them.
 * Assuming one counts the EU as cannon, Han's an orphan, was raised by pirates/conmen and didn't even know about the Force except for what his Wookiee friend from the ship's kitchen told him, which wasn't much. Again, depends on whether you count the EU, but that series doesn't contradict either set of films, so...

Darth Vader wanted the Death Star plans for betrayal.
He considered the Death Star "Insignificant", he knew the Emperor disagreed and would probably decide to make the place his home. Now, let's say Vader wanted the information in a way that would leave no evidence, as to surprise the Emperor when he decided to strike at the Death Star's weakness, thus killing the Emperor. How to do that? Why, take it off someone who had already stolen it of course. Say it was destroyed. That's why he ordered his men not to destroy any pods that may have held the plans, as well as why he didn't simply blow the Tantive IV to pieces. Plenty of problems with this, but hey, Wild... Mass... Guessing...

"Vader betrayed and murdered your father" was not the original line for that scene.
First off, it makes Obi-Wan kinda look like a lying bastard. Second, Mark Hamill supposedly asked George what happened to Luke's father, and was told "Your father and Darth Vader fell into a pit of lava. Only Vader came out." Not only is this a more poetic sounding line, it's also far more "true" than the one in the film. It was probably changed for clarity reasons, or because it and the line about Luke's similarity to his father scaring Uncle Owen combined made the big secret far too obvious.
 * Except that at this time of writing Vader was not Luke's father. It was just one of the many possible plot-threads that Lucas played with in his head.
 * Except that "Darth" was always meant to sound like "dark", in the vein of the old tradition, and "Vader" is the Dutch word for "father". Dark + father. And Anakin was supposed to be the greatest star pilot in the galaxy, and Vader proves the greatest star pilot in the film by far. And he is quite blatantly presented as an unknown man with a mysterious past. Is it just me or has it got to the point now where fans automatically distrust everything Lucas says about his original intentions about anything, no matter how much evidence there is against such accusations? Apparently Its the Principle of The Thing.
 * Also, "confronting the father figure" is one of the universal tropes Lucas learned from Joseph Campbell when consulting him for pointers on building a mythology before he began writing the films.
 * Sorry, but no. The evidence is in the rough drafts of the first two films, all of which are freely available on the internet. In the original draft of Star Wars, the character "Darth Vader" was just an Imperial general -- not a Sith, or even a Force user, but actually much closer to Tarkin -- and the main young hero's father (Kane Starkiller, father of Annikin Starkiller) was a separate main character. In the second draft, Darth Vader had become much like in the final film -- but Luke's father "the Starkiller" was again a separate main character who was still alive and appeared at the film's climax. No "Vader" = "father" connotation. Not only that, but in the first draft of The Empire Strikes Back Luke's father's Force ghost appears on Dagobah -- still as a separate character. It wasn't until the second draft of the second movie that Lucas came up with the idea of having Vader turn out to be Luke's father.
 * I keep hearing such things but I see no proof of them and the whole thing is moot anyway. None of the people who go around raving about George Lucas being some sort of compulsive liar understand the least little bit about how the creative process works, and act shocked and appalled that--GASP!--plans change over time and writers sometimes try different ideas or even come up with last minute decisions! The nerve of the man, not always being consistent about what he wants to do over the course of thirty years! Why, it's almost like artists have some sort of creative impulsiveness at times, or even decide to do things on the spur of the moment, and can't be blamed for changing their minds when they had answered to the contrary off the top of their heads and never promised anything (on the rare occasion that they did say any such thing, which in Lucas's case is apparently less often than not)! Funny also how none of these allegations went around much until fans had already become sore with Lucas anyway because of the prequels. If only you saw how utterly different the first drafts of many of your favorite screenplays were from the finished product--sometimes separated only by a few weeks. If it really wasn't the original plan for Darth Vader to be Anakin Skywalker then at the very least, for the many reasons listed above and others, it was a very lucky coincidence.
 * As far as I know, people blame Lucas not for changing his mind, but rather for not admitting he did so.
 * The proof is out there for those who seek.
 * You actually think I'm unfamiliar with that crap?! Let me ask you this: do you know anyone (including yourself, be entirely honest with yourself about it) who believes in this secret history of Star Wars (that's not a propagandic and sensational, tabloid-like title and concept or anything!) who wasn't already extremely sore at Lucas, or who bought into any of it before The Phantom Menace came out? Not to mention how selectively you're responding to one out of so many points I made, which I made absolutely clear before isn't the most important one at all....
 * Unless you believe the script drafts are forgeries, then is not a matter of "propaganda", it's the objective truth. If Lucas had meant Vader to be Luke's father in the original Star Wars, why would Luke's father be a separate character in scripts for it and even its sequel? As for your other point, the Troper above isn't discrediting Lucas because of the changes in the plot. He's merely pointing out that such changes were made, which, as you say, is often a part of the creative process.
 * If they've kept that line, Obi-Wan's statement in ROTJ would have something like "When he fell into the lava, the good man who was father was destroyed."

Tarkin doctrine would work
Tarkin doctrine would work if the Death Star survived.
 * One rebelling planet destroyed would be always replaced by another until there weren’t any planets left in the Empire. Huzzah for a planetless Imperial victory!
 * Only under the condition that after thirty destroyed planets there still are idiots who couldn´t see what would happen if they start to rebel. At some point it would have stopped.

Obi-Wan wasn't lying when he said "Only Imperial Stormtroopers are so precise."
We all know about the Imperial Stormtrooper Marksmanship Academy. But the, we also know that the Clone troopers didn't necessarily attend that academy; they were pretty damn badass. Obi-Wan went into hiding after the Emperor took over; he may have assumed that the Emperor still used clones, or at least people who were trained well.
 * Wow, this is closer to fridge brilliance than WMG!

Obi-Wan was being sarcastic when he said "Only Imperial Stormtroopers are so precise."
Living on Tatooine for 18 or so years, he probably at least heard about Stormtroopers, so while the above WMG is a great one, it's possible that he noticed the wide spread of the burn marks and meant it as snark, "Only Imperial Stormtroopers are THIS precise."

The Empire employs more saboteurs and Rebel sympathizers than those who actually support the Empire.

 * The guy who designed the shaft on the Death Star must have realized that shaft needed a cover on it or the Death Star would be blown up (his replacement designer did).
 * The guy who says, "Hold your fire!" when the gunner is about to blast the escape pod with C-3PO and R2-D2 on-board either sympathized with the Rebellion or didn't like guns because why else would he be instructing someone not to fire? Are bullets that expensive? This guy must have been a sympathizer.
 * "Hold your fire. There are no life forms. It must have short circuited."
 * "Hold your fire. There are no organic life forms, and there's no such thing as robots, and if they're holding the plans, why would they put them on an escape pod? And besides, no need to waste precious laser!"
 * "Hold your fire. There are no organic life forms, and even when ships are under violent siege, routine spacepod tests cannot afford to be interrupted and are not suspicious at all."
 * "Hold your fire. There might be a passenger on that lifepod, and if we kill them, Vader will kill 'us'."
 * Even Darth Vader is suspect. He concocts the plan to allow Leia to escape, knowing full well that Leia knows about the destructive force of the Death Star - and where it's located. Plus, he still doesn't know what she did with the plans. It's possible that she still had them hidden somewhere on her body, even though we know R2 has them. Either Anakin forgot all of his tactical training or he really wants the Rebellion to win.
 * Hell, the Force Unleashed even shows us that Darth Vader, in a way, helped FORM the Rebel Alliance!
 * What remains of Anakin influenced Vader's sympathies.

Imperial Stormtroopers are more precise than Tusken Raiders.
Jawa Sandcrawlers are essentially skyscrapers wearing thirty foot thick armor on enormous tank treads. If the Sand people attacked, they would have sprayed fire indiscriminately, possibly in order to distract the Jawas from a sand person sneaking onto the sandcrawler unseen in order to shut it down or open it up from inside. Instead, the sandcrawler's outer functions had been completely demolished by high powered blaster fire, far more precisely aimed than a Sand People attack should have been. Questions of accuracy are irrelevant, all that matters is "only Imperial Stormtroopers are so precise."
 * Imperial stormtroopers are actually expert shots. The only times we see them missing is when they're under special orders not to kill (like when the heroes are escaping the Death Star or Cloud City). Their inability to defeat the Ewoks is because that was a totally unexpected situation which their strategies, equipment etc. weren't suited for (compare the United States, a great military superpower, losing to a Ragtag Bunch of Misfits in the Vietnam War).

The Empire is a racist organization.
On the two Death Stars, the only people working are humans, and all of them are white.
 * That isn't WMG. The EU and some of the canon source material make it abundantly clear that the Empire considers all nonhuman species inferior. This may also extend to actual human racism, although that's less clear.
 * During the Clone Wars, the Clonetroopers had darker skin tone, and at least one of them became a Republic fleet commander.
 * They're sexists too, which is why there were very few female Imperial officers.
 * Since the Empire are essentially Space Nazis, it's safe to assume that even without the EU, they're still a highly speciesist and sexist organization. Notice that they refer to Chewbacca as a "thing" and the Ewoks as "bear creatures". By contrast, the Rebels have all sorts of different alien races serving with them and their leader is a woman.

The New Jedi Order tampered with historical documents to make it appear that Greedo shot first.
When Han shot Greedo, he didn't realize he was being taped by the cantina's security camera. Years later, someone recovered the tape and tried to use against the Solo family. Han tried to explain that Greedo had cornered him and announced his intentions to kill him, making Han's shot an action of self-defense no matter who actually shot first. But it wasn't good enough. So someone, possibly R2, altered the tape to make it appear that Greedo had shot first.
 * Simpler explanation: The reason Greedo shot second is because he reflexively pulled the trigger as he died.

Going around the planet to the rebel base on Yavin 4 WAS the fastest way to destroy it.
The original Death Star's main laser had a long cool-down time, so long that going around for a clear shot at the rebel base itself was the faster option.

Luke wasn't the one who destroyed the Death Star.
It was Batman. And here is the photo to prove it...
 * Well, he CAN breathe in space.

Obi-Wan Kenobi had Alzheimer's Disease.
Obi-Wan didn't intentionally deceive Luke about anything, it was from the "certain point of view" of someone with Alzheimer's.
 * Obi-Wan didn’t remember that Darth Vader and Anakin Skywalker were the same person.
 * Obi-Wan didn’t remember owning any droids.
 * He didn't own any droids. Anakin and Padme did. He had an astromech that was assigned to him, and that was it.
 * Obi-Wan really thought Stormtroopers were actually that precise.
 * This one doesn't actually need dementia to be true, though. Remember, he's been on backwater Tatooine, far from even Tatooine cities, since the Clone Wars, before the Troopers accepted recruits from the general population and were a lot better. He may have simply not known about the drop in quality since his retirement.

The medals were given for destroying the Death Star, not for saving Princess Leia

 * That explains why Chewie didn't get one.
 * Because Han and Chewie are such Heterosexual Life Partners, the medal Han received was actually for both of them.
 * Chewbacca didn't get a medal because they are made of chocolate, and you mustn't feed chocolate to Wookiees.
 * Chewie didn't get a medal because it's against his religion.

The Death Star doesn't work properly on gas giants.
The Death Star's laser sets up a massive chain reaction in the planet's core somehow, causing it to blow up from the inside. This fits the image we see of Alderaan. Since gas giant planets are only solid at the very centre it simply wouldn't work, at least not fast enough. It would destroy the core, but the actual gas would take a very long time to disperse. That was why they had to go around Yavin to blow up the Rebel base.
 * Alternately, if the superlaser works like all the other "lasers" in star wars do (that is, some sort of directed plasma or whatever) then perhaps Yavin's gravity well would have effected the beam dispersion if they didn't first clear it. At the very least, I could see the Death Star's gunner as having a reasonable excuse to hold off firing until the last possible moment.

The Emperor put Tarkin in charge to cut Vader down to size.
Palpatine knew that Vader was planning to revolt against him because, well, that's what Sith do. So he occasionally does something to remind Vader that he is subservient. In the case of New Hope he put Tarkin, who wasn't even a military authority, in temporary command of Vader and the Death Star for this very reason.

The Cantina Band keeps playing the same song because that's all they know of that genre of music, and the crowd will kill them if they play their usual stuff.
""You guys know the theme from Rawhide?""

The Stormtroopers can't shoot worth a damn because of the lighting
Look at that visor. It's clearly tinted, and meant to work in a well-lit, outdoor area. And indeed, as Obi-Wan notes, they are very precise when working on Tatooine. However, indoors, it becomes much more difficult to see (hence Luke's "I can't see a thing in this helmet!") - which is why they can never hit the heroes during the rescue of Leia.

Obi-Wan let Vader win because he knew the future.
It's established that Jedi can see into the future, at least to some extent. Obi-Wan knew that Vader would kill the Emperor, which of course he did. He could have killed him on the Death Star, but neither he nor Luke could kill the Emperor. So Vader had to live and that meant he had to die.

Han was lying when he told Luke and Obi Wan that the Falcon made the Kessel Run in less than twelve parsecs
Han had pegged Obi-Wan and Luke to be bumpkins when they hired him, so he decided to pull a random statistic out of his ass to impress or fool them. Eventually he believed his own lie to the point where any Expanded Universe story showing the Falcon's participation in the Kessel Run is just Han's imagination.

Troopers are good shots... on the shooting range. The average stormtrooper is a rookie who doesn’t want anyone’s death on his conscience or in his nightmares.

 * How many opportunities does your standard grunt get to experience killing first-hand, especially on an Imperial space station or on a one-horse planet like Tatooine? Sure, he’ll lay down suppression fire and shoot in the general direction of their targets, but he really just hopes somebody else will actually makes the necessary kill shot. The TIE Fighter pilots are promoted from the ranks of soldiers who have confirmed kills, which is why they’re able to take down rebel ship with much greater accuracy. Since Jawas aren’t human and their faces aren’t visible, killing them isn’t as traumatic as killing Han Solo might have been.

The Death Star was not destroyed at all!
The theory is this: the rebel engineers who found the fatal exhaust port flaw correctly guessed that it would create a devastating chain-reaction, perhaps by destroying some important power relay or control mechanism. HOWEVER, they couldn't have predicted what would happen if the Death Star had a fully charged super laser just moments from firing. The reason we see the "explosion" we do is because the chain-reaction instead re-routed the super laser's power to the hyperdrive, and the entire Death Star was blasted into an Alternate Galaxy/Universe/Dimension! As to the destination....well, (insert fanfiction here).
 * First, they never say the torpedo will go right down the exhaust port to the core, they say that it will cause a "chain reaction" which will destroy the station. I'll come back to this in a moment.
 * Secondly, the explosion we see is all glowy-energy bits, and no actual fragmenting mass like the second one over Endor. A number of EU and fans have mentioned theories such as material being vaporized and/or thrown into hyperspace by the collapsing hypermatter reactor. While this makes sense for the missing mass of the second Death Star, the first completely disappears in a single fantastic flash centered exactly on the core.