We have been trained over many years to look at interfaces whose cues for depth come from a simulated ambient light from the front. This is the case not just in iOS before version 7, but all OS user interfaces. In short, the interfaces from yesteryear have not acknowledged that the true light source of those pixels come from the back, not the front.
The idea that an on-screen UI should behave like it's made of pixels rather than paper isn't a new one, and it makes a lot of sense. Still, it's unsurprising that we've spent so many years attempting to give those pixels the illusion of a physical reality that's anchored in previous technologies. It comes from the same impulse that gave us folders, a desktop and a trash can, from the necessity of providing understandable metaphors for unfamiliar environments. It's a powerful notion that has gripped us for thirty years or more.
This is different. Perhaps the time has come for us to shift our expectations and accept that the language of the screen is its own metaphor, a more appropriate one for an age when children will grow up more familiar with the glowing matrix of LCDs than with the shadows cast on textured paper books. In many ways it's the opposite of skeuomorphic, though it's anything but flat.