I dunno, Cameron didn't do Alien, the film of which Aliens was a sequel. And he isn't the same person he was when he did Terminator 2. His current oral hijinks reminds me more of Lucas about the time he forgot how to make decent movies.
The thing I don't understand is that Cameron's "four sequels to Avatar" is old news -- why are we even talking about it now? I strongly suspect (as I did when this was first announced years ago) that he'll make one sequel, it'll do
And finally, do we all understand that Avatar was made in 2009? Seven years ago?