Fragmentation at the API level is the real problem. Not at lack of "built-in features."
An app written for iOS 6 can run on the iPhone 4S, iPhone 4, and iPhone 3GS (not to mention the iPad 2 and 3, and the newest iPod Touches).
An app written for ICS can only run on those 7% of devices running ICS.
This is how fragmentation works. The only fragmentation happening on iOS is for the original iPhone, iPhone 3G, iPad 1, and the old iPod Touches.
The only one that I don't quite grasp is the original iPad. Running on the same processor as the iPhone 4 and is much faster than the iPhone 3GS. Color me somewhat confused by this one.