Do read Henry Warwick's comment on my post on Roger Dean and Avatar. It makes a lot of sense and has a good link in it. And way to call this issue years ago!
I too am not totally convinced that Dean can successfully sue. You can copy people's ideas so surely you can copy their imagery. Unless there is some more strict copyrighting you have engaged in.
It was rather silly, and disingenuous, of Cameron to talk as if he'd never heard of Dean though. Why not just say "Yeah I love Yes and I love Dean's art" and so on.