Because fighting against a barrage of FUD - largely uninformed FUD - is difficult. I don't know that it's a big enough issue yet for them to address it because as far as I know Vista is the only operating system capable of even supporting Blu-Ray or HD-DVD playback. There are likely very few people who are attempting to use their PCs as such players.
No doubt! this is insane! people complaining! VISTA Allows you watch Blu-ray and HD-DVD it sucks! LOL