NO, NO THEY ARE NOT EXPLAINED. Seriously, NO. For most of these movies, there's little or nothing even attempting to "solve" anything. Clearly this is yet another lame excuse to get page hits by forcing me to look at a slide show. Let's look at the "evidence," shall we?
- Signs: "We couldn’t up with a satisfactory answer. And we’re also wondering how this supposedly advanced civilization never got around to inventing umbrellas or raincoats."
- Gremlins: "It’s never explained in the movie. Also never explained: how this rule is affected by varying time zones and Daylight Saving Time."
- Avengers: "And one with a fairly obvious explanation: Because nobody really needs to see Hulk-junk."
- Demolition Man: "In the year 2032 there is no toilet paper. Not only that, but the proper hygienic maintenance of one’s posterior is done with, yes, three seashells. We were unable and unwilling to spend too much time imagining possible methods—all were terrible beyond comprehension. If anyone has—or finds—an answer, please, for the love of God, keep it to yourself."
- The Empire Strikes Back: "And we just thought of another question: When flying in his X-wing, where—and how—does Luke go the bathroom?"
- The Dark Knight: "We’re guessing it’s because hearing Bruce Wayne’s normal voice coming from behind Batman’s mask is so darn weird and disconcerting."
- Casablanca: DUH.
On the other hand, actually answered:
And this is a nice fanwank:
Independence Day: "We’re guessing that the computer code (and interface) came from the alien ship that the government recovered from Roswell in 1947."