Which is funny after seeing Apple bash fragmentation at the WWDC. Apple has their own version of fragmentation, newer OS versions don't work on older devices.
I, and everyone I know has had a flawless upgrade experience. There have been a couple of exceptions -- the iPhone 3G (not 3GS) suffered with some point releases, but it was a horrifically underpowered device anyway.
When we talk about fragmentation (as developers), we mean API/display size fragmentation. My iPhone 4 doesn't have Siri, but developers can safely use iOS 6 APIs, knowing I can upgrade.
THe iPhone 5 and the 4" display was a step backwards in that regards, but still, you can safely target iOS 5+ and reach about 95% of active, current app-buying iOS users, or target iOS 6+ and reach 90%. But you can't do that with Android (yet) - targeting 4.0+ would lose you a lot of sales.
This will be fixed in the Android market in the next couple of years though, but until then, iOS users/developers/lovers can rightfully boast about "less fragmentation".
