While device and OS fragmentation is still a serious issue for Android, strong sales of newer phones have taken their toll on what was formerly an even split. As late as June, 50% of Android phones were still running 1.5 or 1.6, but that number has been halved and now 2.1/2.2 handsets enjoy a majority.
The numbers are from Google’s constantly updated Android Market tracking system, which collected this data over the weeks ending on October 1st.
25% of such a huge market is still a lot of people, though. I’m still using my G1, for example (yes, I’m part of the problem) and the early push of MyTouch and pre-Droid phones resulted in a lot of users dead-ending at 1.6. We’re still getting updates and apps, of course, but the niceties and speed increases of 2.x have to be looking good to people approaching upgrade time.