Actually I think it's the other way around Mad_guy. But cannot really tell for sure. Just the impression I've got from reading on the subject through the last year. According to this, I've developed the idea Apple holds a larger portion of the patents regarding H.264. But yes, Microsoft also has a chunk. It's no surprise both support it in their browsers.
As for WebKit, I think it should be a matter of time until it starts supporting WebM features. Google's own WebKit-based browser is already implementing WebM and it should be available on the next betas. So they may end up contributing code to WebKit.