This from Cinematical:
"Speaking to press in London, Cameron fully admitted that he's already got plans for two more sequels should Fox want to pull the trigger on them (which they should, because I feel audiences will devour this sucker). Says Cameron (on his pitch to the studio): "So in terms of the pitch it was: OK, you've spent a lot of money on the first one; on the second one we'll be able to amortize it and focus on the story and all that ... and they bought that." If there's one piece of Avatar that people will criticize, it will be the somewhat weak, cliched story -- and so knowing that story will be the main focus of any sequels is definitely a good thing."
Makes sense. All of it. The studio already has the hard stuff hammered out, so why not make a second and third instalment of Avatar? The above paragraph mentions that know they will be able to focus squarly on the story, which is something that has worried me about this weeks upcoming blockbuster release Avatar. So much has been said about the special effects of Avatar. Hopefully, after folks see it, they will not only be glowing about the special effect but also the story. That is what is truly going to bring people back for Avatar 2 and 3.