Well they cast Nikki Reed as Rosalie, so I don't think they're afraid to take some liberties with the characters. Jackson Rathbone, I believe, is also a lot shorter than Jasper is described. Personally I think Taylor looks like the perfect "Twilight" Jacob. He doesn't turn into a giant until "New Moon" and even then, it would look retarded onscreen if they went by Stephenie Meyer's lame "turning into a werewolf turns you into a HOT twentysomething!" logic.