Earlier this year Matt Gemmell defended the flat, buttonless UI aesthetic of iOS 7:

The thing is, we’ve grown up. We don’t require hand-holding to tell us what to click or tap. Interactivity is a matter of invitation, and physical cues are only one specific type. iOS 7 is an iOS for a more mature consumer, who understands that digital surfaces are interactive, and who doesn’t want anything getting in the way of their content.
Nigel Warren calls bullshit:
I appreciate some of their other insights, but I call bullshit on this specific point. Who, exactly, has grown up? In the past 30 years of traditional desktop GUIs, no one questioned the need for basic visual cues to demonstrate interactivity. When it comes to smartphones specifically, billions of people around the world have never used one. To take an example of a particularly smartphone-happy country, almost half the population in the U.S. has yet to buy one.
I’m with Nigel.
The lack of visual affordance in iOS 7 is just one of a handful of problems I have with iOS 7 (Fitt’s Law, anyone?).