X-Wing Rogue Squadron/Headscratchers

Why do the X-Wings in these books use their missiles so much more often than in the rest of the Expanded Universe (or the films for that matter)? They seem incredibly powerful and TIE Fighters have absolutely no defence against them. For that matter if X-Wings are routinely equipped with such powerful weapons why do the Imperials ever risk capital ships against them? Granted a Star Destroyer won't (usually) have much to fear from a single squadron but smaller cruisers and frigates would be sitting ducks.

Depending on the Writer? The power of Jedi throughout the Expanded Universe isn't exactly consistent either, for example, so inconsistencies with military technology and tactics aren't a tremendous stretch. It could also be that because the squadrons in these books are the elite, and they are better at maintaining the necessary unit cohesion for anti-capital ship torpedo salvos even in the thick of battle.
The risk posed to capital ships by missile- and torpedo-equipped fighters is always high in the entire universe, it's just the level of said risk that varies according to whoever's writing. It gets to the point that the imperials eventually design and build a capital ship that has no purpose other than defending other capital ships against fighters (the Lancer frigate, entirely devoid of heavy weapons but with a crapload of anti-starfighter laser guns). And the games turn the whole concept up to eleven... but they're probably non-canon, otherwise it isn't really explainable why other works don't feature entire wings of small craft carrying heavy rockets or space bombs.
The common usage of missiles compared to the films may have something to do with logistics. That is, the New Republic has an easier time producing and delivering photon torpedoes than the Rebel Alliance, so pilots don't have to be quite so frugal with them.