Wil Gieseler’s spot-on observation on iOS 7:

On previous versions of iOS, it was extremely difficult for a developer to implement a blurred background. On iOS 7, this effect is everywhere.On previous versions, using the accelerometer burned through the battery, so using parallax effects was a big energy trade-off. On iOS 7, this has been promoted to a system-level feature, and they’ve optimized the entire OS stack around making this particular feature as battery-efficient as possible.

That’s dedication to skeumorphism.
It’s funny how many of the people bitching about the superiority of “flat” design aren’t arguing it as a design methodology, but as a style.
In iOS 6, UI elements merely look like cartoon-y, physical objects. In iOS 7, Ive has made them behave like elements inhabiting a three dimensional space.
It’s the difference between modifying a Honda to look like Ferrari and building an actual Ferrari.
I’ll take the latter.