As a thought experiment, what if a book with the exact same contents as the HP lexicon were written by a university professor and published by a university press, rather than originating in fan-based website? Would the discussion change, and would Rowling have a legitimate claim? I'm of the opinion that a lexicon is scholarship, whether it comes from official academic channels or not. Also, the idea that the creation of a lexicon is merely the arranging of source material - without any interpretive work involved - is absolutely wrong. The issue of fan communities' involvement only confuses the issue. Just because it's popular literature with a large internet fan base doesn't change anything (can anyone imagine an author of "high" literary fiction, say, Morrison or McCarthy, suing a researcher for making a concordance or lexicon of their work?). I'm not a legally-trained person, so I can't say if Rowling truly has a case. But if she does, that would make a whole lot of what is already in the library infringement as well.

Except this isn't a matter how scholarship, examining the mythological roots of the stories or why Molly Weasely is a subversive feminist icon.

The Lexicon is a cut and paste copy with no original work within.