This is early speculation on my part.
For a while now I've been saying that blu-ray will never take off as a format because it doesn't have a vehicle propelling it. The tech is starting to get cheap enough and enough people have hi-def television these days, but there's no movie that you have to own and that must be owned on blu-ray. Not like The Matrix was for DVD.
Again, this is speculation. I haven't seen the movie yet, but I have a suspicion that Avatar is going to be that movie.