Part of what I think I'm seeing in your comment and elsewhere is people talking about "fanfic" but meaning a particular aspect of fanfiction, as opposed to the genre as a whole.

"Why can't these people do something creative/original" is picking on one aspect of fanfiction. (It's also silly, in my opinion, but that's another rant.) In that context, I think it's perfectly appropriate to point out that many, many other respected works weren't exactly original either. But making that point =/= all of these other works are fanfiction, either.

Does that make sense? I've been chatting about this a lot today, and the brain's starting to go a little fuzzy.