In what way relevant to codecs is the <video> tag expected to be any different from linking to a video file? Chances are that the browser will handle exactly the same codecs with the <video> tag as with URLs visited directly, no matter what the specification said. It's many years too late to be interested in this as a matter of standards. If they wanted to do something useful, they'd provide a way to report codecs in the source URL options in addition to container formats so that browsers can actually tell if they'll be able to play a video without trying it (and maybe finding that it's some obscure codec in an mpeg container, not one of the ones it supports).
If there's anyone who could effectively push open standards in this area, it's the people who do the "Acid" browser tests. If they decided to dock a browser points in Acid4 if it didn't support either Dirac or Theora, or didn't support Vorbis, or didn't support Ogg, then Apple would be pretty likely to come around.