How is the Android OS running?

An Android developers site has posted the make up of the Android consumer base.
It suggests that the Nexus One, which is the smartphone running Froyo 2.2, has only 3% of the market share. However the Nexus One is about to be discontinued.
By far most users are on Android 2.1 making up 55.5% of the market, followed by 22.1% on version 1.6 and 18.9% on 1.5.
XA tiny fraction (0.3%) of OS systems are running on obsolete versions according to the data which was collected over a period of two weeks at the beginning of July.
There is also a table of how many versions the various API's are compatible with. Versions 1.5 and 1.6 are compatible with most APIs while the 2.1 share is growing.


The site states: "Notice that the platform versions are stacked on top of each other with the oldest active version at the top.
"This format indicates the total percent of active devices that are compatible with a given version of Android.
"For example, if you develop your application for the version that is at the very top of the chart, then your application is compatible with 100% of active devices (and all future versions), because all Android APIs are forward compatible."
However this can lead to a problem of fragmentation as picked up in a Guardian article. This is because old versions of the Android OS can't run applications that target more recent versions.
The Guardian says that we don't really know how the Android OS is running because Google won't tell us. Available data on Android market transactions would make the whole picture that much clearer.