Google has made a change to the terms and conditions of the Android SDK (software development kit) to explicitly prohibit developers from taking any action that may lead to the fragmentation of Android. This is the first change to the terms since April, 2009.
Section 3.4 of the SDK terms states: You agree that you will not take any actions that may cause or result in the fragmentation of Android, including but not limited to distributing, participating in the creation of, or promoting in any way a software development kit derived from the SDK.
With such a wide variety of Android devices of different specs and sizes, Google and the different Android manufacturers have had a hard time keeping devices updated with the latest OS. The multiple versions of Android in use by consumers makes developing for Android a much more complex and pricey endeavor. This change marks the first overt step Google has taken to combat this issue.