We have lots of Gingerbread, some Froyo, and ~5% ICS on the market today, with Jellybean coming out again this summer.
What I fail to understand it that each new release is not at all backwards compatible with the previous release.
That is an issue that Google should be addressing. . . but may have to do with keeping the code as small as possible. Retaining legacy code can cause a large amount of bloat in an OS. Ask Microsoft.
It is better in the Apple iOS world, but still not completely backwardly compatible. A lot has to do with more capability of the hardware that the later OS version will run on. . . but at least in the iOS the OLDER hardware is still supported for the most part, if it can be installed. There does come a time, however, when the older hardware simply cannot handle the upgraded OS. . . but, the SOFTWARE has always run. I have never run into a situation where the software failed to run on the upgraded iOS. . . or an easy upgrade did not take care of the issue.
First of all, the naming scheme for Android makes me want to stab my eyes out. It reeks of "juvenile".
Ok, pet peeve aside... ICS has only 5% penetration and they're releasing a new major version of the OS this summer? That seems... odd.