WebM works fine on this machine. mp4 does not. This is why there was a bit of scuffle, as you may recall, about video formats on the web.

Are you saying that WebM, a file format introduced in 2010, is less bleeding-edge than H.264 MP4, a file format introduced in 2003? What definition of "bleeding-edge" are we using here?

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

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.