But again, H264 is not HTML5 video... H264 is a video codec that just happens to be used with the video tag on Mobile Safari and IE9. It's also how a majority of YouTube's videos are encoded currently, as well as many many other video uplod sites.
It's also the codec used on the Xbox360, the PSP, the PS3, and other pes of consumer electronics. It turns out that to reach the largest audience of consumer electronic devices and computer, H264 happens to be the best choice.
Video production workflows let content producers save as h264 videos.
The adult industry is using h264 videos on their web sites to serve their content to portable "more personal" devices.
I'd say h264 is pretty entrenched now.