Google often appears to operate with a chip on its shoulder and seems unsatisfied as it seeks to be everything its chief rival Apple is credited with being. While the company plays second fiddle to nobody, sometimes I believe Google maneuvers with the mindset of a startup by constantly seeking to expand its circle of competence to compete with Apple and now with Facebook.
What is clear is that Google understands what it is dealing with, and perhaps its rivals don't.
Also, the company is positioning itself to be the formidable adversary it needs to be for its own survival. What's more, don't discount that its Nexus 7 tablet and the possibility of creating its own phone via its Motorola (MMI) ownership could have also inspired this deal.
While Facebook's main challenge (among others) continues to be monetizing mobile, Google seems poised to show Facebook as well as the entire market how it's done.