Planet 51/Headscratchers

The thing that bugs me most about this film is that, to me, the only reason it rained rocks was for the sake of that one Singin in The Rain joke with Rover. Plus, how does it happen? Do they live near a constantly-erupting volcano? And why hasn't their town been completely buried by now?
- I must agree.
- I had nightmares due to that shout out.
- According to the Fridge page, it might be a result of Planet 51's ring.
- The town hasn't been buried because workers clean it up, as shown near the beginning.
Rover decides to stay with one of the aliens. I'm sure Captain Baker's going to get raked over the coals for not bringing that expensive probe home.
- Probably not--how many multi-million-dollar probes have we left on distant planets before?
- It was already considered lost, probably, since it had been, for an unspecified time, stored in the aliens secret warehouse. Remember it was already there, and had transmitted info about the planet being barren, before the astronaut arrived.
- Pretty sure bringing a genuine alien lifeform to Earth trumps the loss of an expendable probe.
The lack of pants thing for the male aliens just raised a whole lotta awkward questions about their biology. Made even more awkward by the cork joke, during which Skiff gestured towards where his ass would be... if he were HUMAN, that is. If the location is the same, why the hell aren't they wearing pants?
So, if the aliens have 8 fingers on both hands, they would probably evolve to use base 8 (so digits are 0..7); there would be no "Base 9", nor would they have a word or symbol for any single digit past 7, anymore than we have special words or symbols for hex digits beyond 9. (9 in their system would be 11.)