There could be any number of reasons why there's leftover Aeris coding late in the game, but it all comes down to video game creation being a long, involved, complicated process that isn't always as pat as the final product would lead you to believe. i've heard that one of the developers decided relatively late in production that (SPOILER)rather than make Aeris the final love interest, they'd have her killed and center on Tifa instead. It could just be the remnants of an early possibility that (SPOILER)Aeris be revived, later scrapped. It could be any number of things. i don't know, and it doesn't matter.

The point is, that's junk code - it should have been fixed (removed), but wasn't. Remember the nasty translations that plagued FF7? The game was, after all, a bit rushed, so it doesn't surprise me. What would it matter to leave in some extraneous junk that no one would notice anyway?

But then somebody did a bit of gamesharking, noted her extra lines and her platform at the end of the game, got a little imaginative and started rumors (SPOILER)that somehow, some way, we could revive her. It isn't true.

EDIT: Oops, got a bit off topic. Your best bet for movie FMVs is, as always, a peer-to-peer filesharing network. You illegal pirate, you.