We saw it this weekend. Good movie. Well worth the watch. I like the way the story line progressed. They didn't try to cram too much into it. I don't want to say too much for those that haven't seen it; but the main emphasis was on "the beginnings of the ape revolution".
A valid question that even I was asking myself as I watched it. But again, this is science fiction, and it's about the imagination. And in the movie they "introduce" the scenario that, IMO, ultimately contributes to the decline of the human race and aids the apes in gaining future dominance over their human counterparts.
It's definitely written with sequels in mind.