Fragmentation is like iOS4 isn't available at all on the 2G. The 3G doesn't get wallpapers or multi-tasking. 3GS doesn't get imovie. That's fragmentation.You clearly don't understand what fragmentation means.
All the iPhones use Arm architecture, the A4 is still an Cortex-8 it's just a more customized and power efficient one.
Comparing the graphics chips is like comparing computers graphics cards, the software doesn't care, it may run better on one than the other, but they still use the same code.
The resolution was specifically picked to AVOID fragmentation, as the iPhone 4 shares the same aspect ration and is simply doubled in resolution it can use simple 4:1 pixel mapping to scale the older programs with minimal resources, and likewise the software can be coded to use 1:4 pixel mapping on newer programs to give them functionality on the older phones.
There's a reason practically everything in the app store will run on every iPhone.
Android sets use completely different architectures and non standard resolutions and aspect ratios.
Since Apple won't be able to maintain its momentum when Jobs steps down, I'd say Google will dominate.