Josh at 2011-04-11 13:42:05:
I'm actually taking a psych course that recently touched upon attachment styles and like vs like as opposed to opposite attraction and I think it works in film for the very reason you said. I think it's this challenge or HOPE that we can change, or not even; that things would just work out. Also, it is quite nice to be with someone who isn't yourself.
I would also mention another movie: Eternal Sunshine Of The Spotless Mind, because here we have two opposite personalities and neither of them change that personality at the end, they are still themselves but they still hope it can work. Maybe we just want to be understood, rather than changed, and that reason is the biggest of all when it comes from someone who isn't like you at all. But get's you, and loves you for it.