You saw the film, you fancied the alien, surely you didn't miss them!
Yes at the cinema its HD and 3D, but avatar has pushed the level of detail up a notch, and so I don't think you can fit that much information onto standard blu ray.
Anyway I did some digging and found this
While making copious press rounds to promote his sci-fi masterpiece Avatar, James Cameron has spilled a little bit about his plans for the upcoming Blu-ray release of the film. He has stated that the upcoming disc will arrive this summer and come packed with ten minutes of deleted scenes. He also stated that the first version to hit stores would not likely be in 3D.
That news comes as a warning for true fans, as Cameron plans to re-release another edition of the Blu-ray in late 2010 that will fully support the new 3D Blu-ray players set to hit the market next year. In speaking with MTV, Cameron said that the new deleted scenes give added background to the history of the native Na'vi seen in the film, and there will also be a tribal hunt involving Jake Sully. He added, "It's all wonderful stuff, but it was sort of bogging down the middle section of the movie. There's plenty for a value-added DVD experience on this film. Of course, we'll have to go punch it all up and get it all mixed and stuff like that."
About the 3D Blu-ray aspects of the upcoming releases, Cameron stated, "Probably the initial Blu-ray release of Avatar won't be in 3-D and then a subsequent release will be in 3-D. That's my guess right now. So we will probably put out a disk, you know, in six or eight months, let's call it six months, and then after that we will have a 3-D disc when there are enough sets available."
So it seems you will need a special 3D blu ray player, to get the full experience.