I was surprised too when I saw the new Marketsaw article on Avatar as of late.
According to an interview with James Cameron, Avatar 2 may have some elements of a prequel, which could explain why Sigourney Weaver's character, Grace Augustine will be coming back. The entire plot seems like it might be non-linear, showing stuff that happened before Jake came to Pandora.
Here's the article:
MarketSaw - 3D Movies, Gaming and Technology: James Cameron Update!!

