Affordance is one of the universal principles of design. Lego blocks' male/female surfaces naturally afford plugging them into each other. Door handles naturally afford gripping them and pulling the door open. It is a powerful principle when used properly.
And while the problem with the old (classic?) iOS was overusing (and abusing) skeuomorphism, the problem of iOS 7 may well be the lack of affordance. You cannot trade how surfaces look with how elements interact. They are not interchangeable. Interactions are dynamic -- they happen while you work with the interface...
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.
