> With Chrome(ium) you can just replace the copy of the libavcodec dll/so, and it magically supports whatever codecs the new one is built with.

Yes, that is exactly what every non-technical user is going to do to get HTML5 video working properly in Chrome. If there was a button that popped up saying "Get the h.264 codec for Chrome" whenever there was the possibility of using it, then we'd have a comparison, but I doubt replacing shared libraries underneath Chrome is ever going to be a supported mode of extension.

It's what linux distributions have been doing by default — just replacing it with a symlink to the system's installation of ffmpeg. The sane ones take the added step of not crippling their default ffmpeg :)

Unlike Firefox, Chrome extensions are sandboxed, so they can't automatically replace the file for you. Someone can just make a simple native installer to do so though.

Still, the tide appears to have turned, so the usefulness of restoring h.264 <video> support may decline within a year. People outside the Mac world will probably just standardize on a Flash video player instead of trying to support multiple playback frontends.