Though it may look to be a Google stride into handsets, I think pretty much their hand was forced due to the patent situation they face currently. Couple of situations:
(1) Moto's Sanjay Jha has at least on two occasions reiterated using IP as a differentiator (read use IP to become a patent troll). Techdirt published a piece months ago where the headline was "Motorola's Best Play Is To Become A Patent Troll & Destroy Android Ecosystem With Patent Lawsuits". Also considering Motorola is already embroiled in lawsuits with Apple and MS, while Symbian, BB and WebOS pretty much non starters at Motorola, the only place Motorola could monetize its vast patent repository is the Android ecosystem. This could lead to a slippery slope for Android adoptees and hence the Google intervention possibly.
(2) I recently read that there is glaring non compliance of GPLv2 source code disclosure requirements w.r.t the Linux drivers and kernel in Android. Here is an interesting blog post by Ed Naughton that dissects the core issue. This has a potential to damage existing adoptees big time.
With these serious issues hanging around Android, plus the Oracle/MS/Apple lawsuits ready to undress Google, it makes sense that Google would want to stop the hurt with an existing partner with investments in Android and also in the process get access to the much needed war chest of patents which it seriously lacks.