I think that Mac OS X unredirects unoccluded windows; I've noticed windowed computer games suddenly getting much slower when I move another window in front of them.
It appears to, or has some other trick... My coworker has a huge monitor, and his MBA doesn't hit 60 FPS on any of the fullscreen animations, but individual window contents can go at 60 making me think they don't repaint the world every time a window changes.
