They should care because the H264 patent expires in 2025. If we were looking at a few years then you might be right not to worry. It's odd that MPEG LA supporters are coming out of the woodwork on this issue, seemingly to prevent HTML5 from starting out on the right foot.
"The" H.264 patent? I have, sadly enough, the MPEG-LA agreement here, and there have got to be 25 pages at least simply listing patent numbers, with expiry dates ranging from very soon to a long time from now.
MPEG LA supporters
So everyone who is against Mozilla's attempt to force crappy software on us using the excuse of patents is an "MPEG LA supporter"? Some of us simply don't care about patents, as hard as it might be to believe for some.
I understand. But you could have a replay of the Unisys GIF situation except that it will last a very long time. Most developers and web services (vimeo, youtube, etc) are only thinking about how to improve their product in the short term. The best short term move is to choose H264. They're free to do what they want. So is Mozilla. Those same web services will screw themselves if they make Mozilla irrelevant. But again, short term thinking.
How will they screw themselves by making Mozilla irrelevant?
It's not like Mozilla in any way had any influence on their websites becoming popular, nor will they be affected at all if browser user agents change from Firefox -> Chrome.
Right now: Firefox is the only platform-neutral web browser. Firefox on Linux and Firefox on Windows are supposed to be the same browser.
Using OS codecs changes that, which means a Windows shop can test Windows browsers, but no (reasonable) way to test Linux browsers.
So long as there is a platform-neutral browser, browsers have to work similarly.
If you remember: Microsoft IE for mac and for windows operate so differently that they must be developed for as separate browsers, and yet banks regularly told people to use IE (despite the fact that IE on the mac didn't work either- and the bank programmers had no way to test it).
Content producers earn on eyeballs, and if 10-50% of their users aren't seeing what they want them to see, they'll adapt: browser sniff, flash fallback, or whatever it takes.
As a result, video will remain complicated. Maybe Apple and Microsoft can be pressured into supporting OGG, or maybe their users can be prompted to get higher quality video by downloading some codec or plugin. Maybe a technology like ChromeFrame will become popular.