The proof of sales does not mean everyone liked it either. I contributed to the eighty-bajillion dollars Avatar made and I most certainly did not enjoy it. There are a number of people in this thread who agree with me. The door swings both ways. Just as I can't say everyone hated it, just by throwing numbers around you can't prove everyone loved it. Some people did, some people didn't.
It was a new spectacle when it was released, something folks hadn't really seen before. That level of surprise will be hard to duplicate when the sequels come out. Sure, they might be beautiful but they'll likely never be able to recreate the wonder of the first film. I do think Imagineering and the people from Cameron's side of the fence will be able to create something that transcends the films. But by the time that this area opens I imagine it will be the wonder of the theme park elements and not the film tie-in that will draw visitors in.
Avatar has made a ton of money, sure. But at this point in time it is impossible to judge its long term viability. Despite all of its potential, I still feel this is a shaky business decision in the long run. Nobody, however, supporter or detractor can say if this is going to be a success. We've seen no art and no announcements about content have been made. Heck, at this point the whole thing may end up scrapped. If the bean counters at TDO and Cameron come to an impasse on budget or the like, Avatar-land could become Hyperion Wharf 2.0.