The Android platform is a quick moving one and, while Google does its best to keep the OS fresh and safe, OEMs and carriers don’t always act quickly in pushing out the latest code to already existing devices (new devices are also being pushed to the market with code that’s not always the latest).
At this moment, the situation is as follows: six versions of Android coexist on devices (Cupcake, Donut, Eclair, Froyo, Gingerbread and Ice Cream Sandwich) with Gingerbread being the dominating one. Android 2.3.x represents 50.51% of all Android installs while the rest of the versions still account for a total of 47% (the difference is Honeycomb on tablets). In layman’s terms, for every Gingerbread phone out there thers’s a phone running earlier code.
While Ice Cream Sandwich is too fresh to be part of the pie chart, Froyo still has a whopping 35.3% with Eclair running on 9.6%. There are also 1.3% of devices running Donut and, believe it or not, there are 0.8% phones powered by Cupcake.
While it is fair to write off Cupcake and Donut phones, the future should see a shift from Froyo to Gingerbread and from Gingerbread to Ice Cream Sandwich (in some exceptional cases, directly from Froyo to Ice Cream Sandwich). We have to also accept the fact that some devices out there are doomed to run the current version of Android until they’re trashed. The only question is how quickly will OEMs and carriers act on this.
Source: Android Developers