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This report disagrees with you rather strongly:

It claims 2.3 and 2.4 make up for ~75% of the installed base, and the remaining 25% is just a mess.

The official dashboard is http://developer.android.com/about/dashboards/index.html and has been updated fairly often - maybe once a month or so - since ICS released.

According to that chart, about 84% of devices that have accessed Google Play are on Froyo or Gingerbread, and another 7% are on ICS.

Pretty much all of the phone market is concentrated in Gingerbread and Froyo. I think fewer than 10 types of phone are on ICS.

Sony alone moved about 10 differen models released in 2011 to ICS about two weeks ago, mine among them.

This is true, but typically you will decide your minimum API level. A lot of apps moving to 2.0+ API level minimums in order to reduce the clutter.

However, compared to hardware variations and manufacturer/carrier modifications, API level is a piece of cake to handle.