I think the idea was to keep a defensive portfolio of patents so Google could threaten to countersue Apple or Microsoft if they ever went after an Android OEM. Kind of like a Tech company version of a nuclear deterrent.
Yes, although everything that I've read suggests that Motorola's patent portfolio was light on anything related to smartphones so it provides little in the way of a litigation deterrent for competitors of Google or Android OEMs.
That argument seems shallow, though, you could use it to say was incredibly effective - Android OEMs didn't get sued after that!