Considering that the "Android OS" portion of the graph includes all Android-based devices, and the whole issue of Android platform fragmentation has been discussed to death on here and other places, I'm going to have to disagree with you.
There are actually a great deal less of Android devices than iPod Touches. Touches have been out many more years, they are relatively cheap, and they are not tied to a contract. They likely make up a great proportion of the graph you posted. Geez, every high school kid and their Mom has a Touch.
As for fragmentation, I don't see how this plays in the conversation. Androind 2.0, 2.1, or 56, doesn't matter, still an Android. Just like iOS 2.1, 3.0, and 4.02 (all examples of iOS fragmentation - not everyone upgrades and certain apps can only be used on certain versions/iPhones) are all iOS.