[smackfu]

The introduction date of the format doesn't seem very relevant, since what we are talking about is native inline browser support.

[chc]

Same story. Most browsers supported H.264 first (because it was dominant before WebM was even born). Internet Explorer, Safari and MobileSafari still do not support WebM. I don't see any reasonable way to say that WebM is well-established and H.264 is not.