"I considered requiring Ogg Theora support in the spec, since we do have
three implementations that are willing to implement it, but it wouldn't
help get us true interoperabiliy, since the people who are willing to
implement it are willing to do so regardless of the spec, and the people
who aren't are not going to be swayed by what the spec says.
"
That appears to be the permanent fate of the World Wide Web Consortium and its specs, unfortunately.