While Google is inching towards bringing an end to the Android fragmentation with version 4.0, Apple and Windows Phones have started to show fragmentation.
Windows is the most fragmented mobile platform. So much so that popular games and apps are not capable of running on the new handsets.
The new entrant is iOS which is making it increasingly painful for users to find that most of the new features won't work on their devices, even if they are running the latest OS.
iPad and 3rd generation iPod Touch will not be getting any iOS 6 upgrade at all. Even the devices which will be upgraded to iOS 6 won't be getting all the 'new' (already found on Android) features.
According to The Verge only "(the iPhone 4S, iPad 2, and new iPad) will be able to use the new Flyover and turn-by-turn navigation features in iOS 6."
iPhone 4 won't be getting the Facetime over cellular networks feature whereas iPhone 3GS will miss quite a lot of features including shared Photo Streams, VIP and flagged email features, and the offline reading list.
It is unclear why Apple won't bring these features to other iOS devices.
So there is a three-tier fragmentation in iOS walled garden -- devices which will not get any iOS 6 updates, devices which will get iOS 6 update but won't get any new feature and devices which will get iOS 6 + features.