Older phones are being updated, retired or just plain outnumbered by smartphones running Android 2.x
Last month, under 80% of Android users were on 2.x devices, so the upgrade march continues. Most of the gain was in Android 2.2 devices, which have some significant advantages over their 2.1 counterparts, including Voice Actions, faster browsing, enterprise features, and Google Docs editing, among others.
Movement since June below:
Interestingly, if you add the above numbers up there is 0.1% missing. Surely that could be due to rounding, but I like to believe that those are the Android 2.3 devices being tested in the wild.