Android OEMs should hear Microsoft, Nokia out on Google-Motorola combo (ars technica)

While it's impossible to know how this will affect Google's relationship with other Android OEMs, I think the most likely (and sufficient) reason for Google to buy Motorola is to acquire patents to fend off lawsuits from Apple, MS, etc.

My understanding of Google's interest in promoting Android was to ensure their penetration into the mobile sector. Without some leverage, they might have have been squeezed out (or taxed) as a service and content provider by the platform companies.

I suspect Google knows (particularly given the lackluster success of its own mobile hardware) that a robust ecosystem of OEMs is necessary for Android's continued success.