The idea that WebM is a "more open standard" is effectively Google propaganda. H.264 was developed by the Moving Picture Experts Group (MPEG) and the Video Coding Experts Group (VCEG), which are standards committees that draw members from industry and academia under the umbrella of the International Organization for Standardization (ISO) and International Telecommunication Union (ITU), which are (in practice) intergovernmental public/private partnerships. It's is governed by a multi-party governance process representing many different stakeholders.
It's a real open standard. Does it require patent licensing? Yes. But that's not because (as some people seem to think) it was developed by some company that licenses it out to make money. Rather, it requires patent licensing because it turns out that a lot of the techniques you'd want to use in a modern video codec are patented, so the standard that MPEG/VCEG created ended up infringing on a bunch of them -- about 1000 of them, in fact. As is common with such things, a patent licensing pool was set up to make licensing all of those patents easy for implementors.
It is extremely unlikely that WebM does not infringe on some of those very same patents. It's a very similar codec to H.264. Moreover, this has happened before. Microsoft's VC-1 codec was supposed to be a patent-free alternative to H.264, and guess what? It ended up requiring a patent license pool as well.
So, with H.264 you get a codec that's an actual open standard, with a formal multi-party governance process and with easy patent licensing. With WebM, you get a codec that's not formally standardized, has no formal governance process (and is de facto controlled by Google, because they employ most of the developers), and that has huge 'submarine' patent risk.
And Google has managed to convince people the latter is a "more open standard".