How does iOS 7 implement the UI elements so that they look different depending on what SDK you compile with?

Question

There are elements like UITableViews, UINavigationBars that have a different style on iOS 7.

This style is determined at run time, since those

Answer 1

Without going too much into NDA'd territory, I'd just like to state that yes, they are conditionalizing appearance and behavior based off of the result from the following call:

_UIApplicationUsesLegacyUI()

This function, in turn, makes a call to GSApplicationUsesLegacyUI(), which I presume returns a result based off of the version of the linked UIKit.

This means that yes, they are conditionalizing parts of UIKit for legacy. Not sure that's a good thing, but that's what they decided to do.