Google enforces compatibility.

So it turns out that Google has foreseen the potential for fragmentation opened up by the use of the Apache License v2, and strong-armed the OHA members into compatability.

ZDNet.co.uk is reporting that Google has confirmed that the members of the Open Handset Alliance have signed a "non-fragmentation agreement" compelling them to not modify the code in non-compatible ways. Of course, as ZDNet's unnamed source (a "Google spokesperson") notes "That is not to say that a company that is not part of the OHA could not do so."

Whether or not Google could enforce such an agreement in the face of reality is another question. As John Delaney of IT consulting firm Ovum says in the article:

"It sounds difficult to specify and to enforce...Fragmentation is to some extent chicken-and-egg. It is caused by vendors wanting to get a competitive edge, but also by consumer choice...That situation isn't going to go away as a result of anything Google has announced."