"Fragmentation means that the platform is divided into multiple incompatible versions."
You are describing only one aspect/axes of fragmentation: Operating System fragmentation. To really have a discussion of Android's fragmentation you have to take into account the entire mobile ecosystem. You must consider the fragmentation across 5 axes:
- User Interface
- Device
- Operating System
- Marketplace
- Service
FWIW, I wrote a piece that explains this taxonomy:
http://ceklog.kindel.com/2012/01/14/fragmentation-is-not-the...
That is not the case here: The Android team does a pretty good job in keeping Android forward-compatible. That means that right now, more than 93% of all Android devices can be targeted by the same API (Android Eclair).
What the author is actually analysing here is the penetration and legacy of new versions of the cross platform technology Android. How fast are manufacturers creating and updating operating systems that are based on a new version of Android? But that's not fragmentation.