From an Entertainment Weekly article, direct word from James Cameron about the Avatar Blu-ray I've got sitting on my desk:

"There's zero extras! There's so few extras that you put it in, you push play, and the movie starts. There are no trailers, there's no bullshit at the beginning that you have to endlessly go through. I have a deal with the studio and it goes like this: Any movie I make that makes over a billion dollars goes out without a bunch of crap trailers for your other movies."

I frankly approve of the upfront bluntness as to why there are no extras on this release. It makes sense, and it's not like they're pretending this is the only one ever and then surprise everyone with another edition later. He's laid out the roadmap.