The Idea of Ideas and IO9's interest in Avatar

From the article titles alone, IO9 appears to like Avatar with a desire to have it shell out money to certain parties.

• James Cameron explains Avatar 2 delays: “I'm living in Pandora right now” My interpretation: Avatar 2 is coming--Yay!  
• The Complete List Of Sources Avatar's Accused Of Ripping Off.  Example quote: "Is there a case? James Cameron came out and admitted it, last summer." Which sounds like a direct conviction of Cameron in the court of IO9; however, it gives Cameron a say, "I just gathered all this stuff in and then you look at it through the lens of science fiction and it comes out looking very different but is still recognizable in a universal story way."
• A History of Plagiarism Claims Against James Cameron.  My interpretation: Cameron has a history of ripping people off, so he's probably guilty.
• Did Prog Rock's Greatest Artist Inspire Avatar? All Signs Point To Yes.  My interpretation:  guilty!  However, the title is a pun.
• Avatar Sparks New Interest In The Strange Visions That Inspired It.  My interpretation:  Additional evidence!  I suspect the article is merely intended to celebrate Roger Dean.

The authors seem semi-unbiased--Charlie Jane Anders appeared to place little stock in the claims in the comment section: "you could easily do a list like this for Star Wars. It's just funny how eager people have been to point out what sources Avatar 'ripped off.' "  But the titles as a group do accidentally lead us to the subtext that Cameron is guilty.

This brings up a slew of questions:  Where's the demarcation?  What is plagiarism?  What's coincidence?  What's homage?  What's wrestling with other people's ideas?  The waters get murky because if you've studied genre history and/or studied with James Gunn, you learn authors actually responded to one another's ideas.  For example, Tom Godwin's "The Cold Equations" still has writers arguing with him.  As does Robert Heinlein's Starship Troopers, which has some of the biggest names in the business respond:   Joe Haldeman, Orson Scott Card, and John Scalzi.

With Robert Sheckley, I discussed the similarities between Stephen King's Running Man and Sheckley's "The Prize of Peril".  Sheckley said he had called up King and asked about that.  King admitted he'd read the story and admired it, but it had been awhile.  Essentially, grist for the mill.  Sheckley accepted the answer.  What a generous heart that man had.

Most likely the articles are intended to provoke thought and discussion although I can't help but feel some sympathy for the artist and wonder what's next for art, especially as copyrights keep getting extended indefinitely.