I don't have proof, but the way it went down.. I believe James Cameron said he'd made claims to "Avatar" years previous with something written already or..something equally stupid, so the people making the new series had to go with a title change.
Yeah.. just looked it up, he had it trademarked, and actually came up with it in 95-96 with the script.. so yeah. I think it's retarded as fuck he did that to Avatar: The Last Airbender and what not.. but alas. That's why the movie (terrible as it was) didn't have "Avatar" in the title.
But yeah, I'd say casual fans will still know based on Mike and Bryan.