One thing that would have been nice, and I'm not sure how feasible this is:
Is if either HD-DVD or Blu Ray had mandated a DVD stream embedded in the disc, or somehow downscaled itself so that every disc worked in a DVD player at 480i.
The hd-dvds I have look amazing on my hdtv, but they offer me no value outside of my living room, or others who might own one. I can't take it on my video ipod as a consumer (well, thanks to copy protection I could, but the average consumer couldn't,) I can't play it in portable dvd players in a car, or at a friends house that only has a dvd player.
If either of these discs had been able to offer that to the consumer at no extra cost (and not in a shitty flipper format, although that's better than nothing) then that would have been great and really helped mainstream adoption. Because of that, unfortunately it's going to take a lot longer for some people to make the switch. I agree that once you see HDM vs upscaled dvds there is no argument, but it will take a long time, if ever for Blu to really take the place of dvds.
Simply because people can already play DVDs in so many ways, while even if you did have a blu ray player in your car, would your screen even be good enough for you to tell much difference? This means people will have to either buy a blu player for travel/car/airplane (although laptops would benefit from blu drives obviously) or buy two copies of the movie. Some will choose to stick with their $5-$10 dvds, and frankly I can't blame them.
Edit: as an hd movie lover, I'm glad Blu won, even though I went red originally. I think and thought Blu was better for the movie and computer industry especially. When you're talking about the difference of being able to back up an extra 20 gigs a disc, it was a no-brainer. Not even considering the possibilities for longer movies like LOTR at potentially better quality (higher bitrate encodes.)