There are so much awesome APIs on iOS 7 that we planned to leverage in the future, cutting off legacy platforms simply help us focus on looking ahead instead of backwards.
At first glance, it appears to be doing a lot of UIKIt Dynamics stuff, and that only came to 7.
Using the new keyframe animation API by the looks of things.
Yes it's using the keyframe APIs, it might be more like an experimental code style for now, but we will keep revising to make it better.