This screen-as-object paradigm is easiest to understand in the multitasking interface, where each application is laid out in a row. At first glance this looks like the old app-switcher UI with the added bonus of a preview of each app. But notice that when one app triggers the opening of another app, the new app now actually slides in from the left. If you need to switch back, double tapping home zooms back out to show the original app to the right. This creates a new consistency of interaction that was not there previously. Switching apps is now a much more coherent experience that can take advantage of your spatial memory.
David Cole, Product Designer at Quora makes some very interesting and insightful comments about the way that iOS 7 makes better use of our spatial memory to help us navigate. I particularly enjoyed his reference to Jef Raskin's Zoomworld UI, which I've long admired.