"Overall, VP8 appears to be significantly weaker than H.264 compression-wise. The primary weaknesses mentioned above are the lack of proper adaptive quantization, lack of B-frames, lack of an 8×8 transform, and non-adaptive loop filter. With this in mind, I expect VP8 to be more comparable to VC-1 or H.264 Baseline Profile than with H.264. Of course, this is still significantly better than Theora, and in my tests it beats Dirac quite handily as well.
...
Finally, the problem of patents appears to be rearing its ugly head again. VP8 is simply way too similar to H.264: a pithy, if slightly inaccurate, description of VP8 would be “H.264 Baseline Profile with a better entropy coder..."
I won't pretend to know what all of those terms mean off the top of my head, but if the lead x264 developer sees absolutely no technical advantage in WebM vs. h264, that sounds pretty damning to me.
As for why x264 encodes h264 so much faster than ffmpeg or whatever encodes WebM, the simplest explanation would be that there is much greater demand for an optimized h264 encoder. WebM has some admittedly large users (Wikimedia Foundation, Youtube for browsers with no h264 support and no flash player, and now 4chan), but they're still vanishingly small in comparison to the users of h264 ("the entire video industry").
