All it takes is for h.264 to infringe one patent that Goggle holds and they are stuffed. Google could then simply require for licensing their patent that any patents held by MPEG-LA against VP8 to not be enforced against any implementation of VP8.
This does seem like a potential approach that Google might take. After all, the licensing terms for the WebM codec seem to (IANAL) boil down to "You can use WebM completely freely, unless you sue us for IP infringement, in which case you lose your license to use our stuff". From the WebM license page:
Google hereby grants to You a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable (except as stated in this section) patent license to make, have made, use, offer to sell, sell, import, and otherwise transfer implementations of this specification where such license applies only to those patent claims, both currently owned by Google and acquired in the future, licensable by Google that are necessarily infringed by implementation of this specification. If You or your agent or exclusive licensee institute or order or agree to the institution of patent litigation against any entity (including a cross-claim or counterclaim in a lawsuit) alleging that any implementation of this specification constitutes direct or contributory patent infringement, or inducement of patent infringement, then any rights granted to You under the License for this specification shall terminate as of the date such litigation is filed.
(The above text by Google from the WebM license page seems to be licensed under the Creative Commons Attribution 3.0 Unported License)
I'd be surprised if Google didn't have some expert IP lawyers working day and night on this issue, because it's definitely in Google's interest to have a free and open video codec out there. Let's conduct a thought experiment. Which would be more expensive for Google: paying MPEG-LA licensing fees for using all H.264 videos on YouTube, or capacity for a slightly-more-bandwidth-heavy VP8? (Bonus points: by how much?) Of course, this is besides the point: Google generally benefits from an open Internet, so I wouldn't be entirely surprised were this were just one of their general pushes in that direction.