Versions of the Google Android mobile operating system are forward-compatible, but not backward-compatible. That means that an app developed for version 1.5 will work on version 2.2, but the opposite is not true. Because of that fact, developers face a difficult balancing act: they want to be able to take advantage of the newest features in the OS, but they also want to reach the biggest number of users.
The latest Android figures from Google should make that decision a little easier. While only 3.3 percent of users are running the latest version (2.2, aka “Froyo”), 55 percent are running 2.1. Most of the rest are split between Android 1.6 (22.1 percent) and Android 1.5 (18.9 percent).