I've always been curious as to why Google doesn't at least rty to indemnify Android OEM's by working out some sort of agreement with Microsoft. I'm almost certain Apple and Microsoft have cross licensing agreements in place with regards to their respective mobile patents
I expect an individual OEM can get a much better deal out of Microsoft than Google could.
Remember, Microsoft doesn't care (much) about the money. The more important value of the Android patent racket for them is in making Android less competitive to defend/promote Windows, Windows Phone and Windows RT. Doing a deal with Google cuts against that, so Microsoft would (rationally) ask for a lot.
On the other side, going after OEMs one-by-one creates FUD and puts more pressure on Google as each OEM domino falls (especially when the various licensing agreements need to be renewed). Plus, unlike Google, most OEMs have significant Microsoft-related product lines whose licensing and promotion costs can be used to obscure the true economic substance of any licensing agreement.
On the other hand, I suspect that when it comes to the nexus of IP and Android, it is in their legal interest to avoid every appearance of Ownership and Authorship. I.e. Google has no interest in claiming responsibility for anything connected to patent violations.
It's no different than Apple not indemnifying developers when they were sued for violating patents a couple of years ago...except that Microsoft and the companies licensing their patents have legal teams similar to Google's.