That's because you are framing the issue as something it's not. It's not fragmentation in the same sense as Android. 93% of apple devices are on the latest iOS version. Right around 30% of Android devices run the latest major release. The number is actually quite a bit lower if you start to consider point releases. Even worse is the fragmentation caused by different vendors and chipset manufacturers writing different libraries and drivers. See libstagefright, which has major differences across different devices even if it's the same version of the OS, for example different native pixel formats are supported by different vendors so writing any kind of a custom protocol video streaming app on Android is a stone cold bitch to get working across devices at 60 fps and that's only targeting 4.0+. It gets way worse when you include older versions that may or may not have libStageFright (most 3.0+ have it but a few don't). I'm familiar with video and audio the most but other areas have the same issue.
Contrast that to iOS, sure different API's get added but at least the same versions of the os behave the same across devices. Sure for a very short time iOS will be split between versions but that will be exceedingly short and you'll never have the true fragmentation problems that Android has in iOS.
Contrast that to iOS, sure different API's get added but at least the same versions of the os behave the same across devices. Sure for a very short time iOS will be split between versions but that will be exceedingly short and you'll never have the true fragmentation problems that Android has in iOS.