But, if the original poster's speculation were true, it would put Google in the traditional role of a technology patent holder who holds a defensive arsenal of patents: if MPEG-LA makes a fuss about aspects of VP8 which they claim infringe MPEG-LA patents, then Google can threaten to retaliate by suing everyone in the world who is currently shipping an implementation of H.264 for infringement of the On2/VP8 patents (and so publicly demonstrate the fact that being an licensee of the MPEG-LA H.264 pool doesn't protect one from all patent claims, and provides no insurance or indemnity).
Stalemate. Mutually-assured-destruction stand-off. Result: VP8 available for royalty-free for use, without MPEG-LA interference.
But only if Google really have inherited some killer On2 patents as part of their acquisition. I hope they have - it would make sense of their strategy and confidence in VP8 if this kind of thing were going on in the background.