Dan Wineman, with an interesting counterpoint to the benefits perceived by iOS 7’s depth:
iOS 7 may be “trading” affordances for kinetics, but only in the sense that it’s losing the former and arbitrarily gaining the latter. They are not interchangeable. Kinetics, or UI Dynamics in Apple’s parlance, are visual effects that occur while you interact with an object, or afterward. (You pull up on the camera icon and let go, and the lock screen falls back down with a realistic bounce; you scroll quickly in Messages and the word bubbles act like they’re mounted on springs.) But affordances can only help if they appear before you interact. You need to see the handle to mentally feel how to open the door, or even to know that it’s a door in the first place, regardless of how smoothly it’s going to swing open. In user interfaces we call this trait “discoverability.”
I’d argue though that iOS 6’s interface wasn’t anymore discoverable than iOS 7’s. In both cases it is pixels beneath glass. Is an arrow really less intuitive than a grip handle?