Microsoft tends to license or indemnify OEMs paying them a royalty for Windows. Like for instance, Google is currently suing Microsoft for patent infringements in Windows, but not HP or Nokia because Microsoft indemnifies their use of Windows (takes all the legal liability from them). Google does not do this for Android. So it's possible Android OEMs are also paying a bunch of other random companies for patent rights that they wouldn't have to if they just used Windows.
Google Pay TRION $ to Samsung ;)