One of the major staples of Android development's always been the operating system's ability to automatically scale apps up and down in order to accommodate whichever form factor they're being used on.
Apple's approach to form factor fragmentation has traditionally been the opposite one. As in, Apple requires app developers to target each screen size with a pixel-perfect user interface. Though iPads can pixel-double tiny iPhone apps, Apple wouldn't degrade user experience by letting iOS stretch apps' hard-coded interfaces.
It would appear that iOS 6 introduces a diametrically opposite approach, one letting developers construct interfaces that can intelligently adapt to different screen resolutions without looking plain fugly.
This is not just convenience, but a necessity given that rumored taller iPhone and an iPad mini, both allegedly due around September or October of this year...