One other challenge related to different device sizes is that designers cannot create a pixel-perfect design in Photoshop and send it off to the developer. They have to be aware of how the interface components will resize and shift around as the aspect ratio, resolution, and screen size changes.
Designing for responsive layouts should be second nature for designers dealing with Android. The same issues appear on web in much more dramatic fashion.
You would assume that web desginers and graphic designers in general have been around much longer than iOS though. This is not a "new" problem which haven't already been solved.
Being too iOS-centric in this space will severely limit your capabilities as a developer and designer.
