Have you read the Harry Potter series? If you have, you would know that it has an incredibly deep backstory, with dozens and dozens of characters - some of which are only lightly mentioned in the books themselves. In order to do a harry potter lexicon justice, it would have to include information on all of these characters - going all the way back to before harry was even born. The ONLY person who knows that information is JK Rowling and hence she is the ONLY one qualified to write that book.

On a legal note, since she/warner bros. owns the Harry Potter world, she has every right to defend someone else publishing a harry potter book, as it probably would violate any exclusivity agreements she has with her publishers and or Warner Bros. That would create legal trouble for herself.

Bottom line is it makes sense to block this book from being published by third parties.
http://aoleonthemartiangirl.com

There's actually rather a lot more to this story that, for some reason, isn't being reported by Salon and other sites. JK Rowling and WB were perfectly happy to leave the HP Lexicon alone when it was a website serving fans for free, and JKR even gave it some award on her website. The problem arose when the guy running the site wanted to publish it as a book, directly competing with the official encyclopedia that JKR is working on and using a lot of her work for his own profit.

A great deal of content on the Lexicon was copied directly from the book "Fantastic Beasts and Where to Find Them," infringing on JKR's rights (note that I am not talking about critical commentary or analysis, but actual, direct transcription of the book). There is a lot of information copied directly from the other books too, but the "Fantastic Beasts" copy is the most blatant. Also, the UK cover of the proposed Lexicon book looked almost exactly like the UK Harry Potter book covers, thereby implying it was an authorized encyclopedia.

Additionally, RDR Publishing have done the following things: refused to provide a copy of the book to JKR and WB's lawyers, at one point actually saying, "If you can't figure out how to hit 'print' on a website, have someone on your staff do it for you;" stated that the book was typeset verbatim from the website, then later said it was a completely different book that contained "critical essays," for none of which they contacted the original authors asking permission to reprint; compared being sued by WB and JKR to being in Hiroshima and Nagasaki when the bombs dropped; asked the judge for seven weeks' continuance on the case so that their lawyer, the publisher's cousin, could have time to read up on intellectual property law; accused WB of bearing false witness in an official court document; stated their intention to publish regardless of the outcome of the lawsuit (this was before the injunction blocking publication)... the list goes on. These are not the actions of a company who has any sense of what the copyright and fair use laws actually are.

(Well, the Hiroshima/Nagasaki thing doesn't really reflect on their knowledge of IP law, just their general tackiness.)

Steve Vander Ark, the book's editor, at one point told other would-be encyclopedia publishers in the Harry Potter fandom world that "basically, it would be illegal to sell a book like that." In addition, he posted a message in 2000 to a Harry Potter mailing list saying "Thanks for you kind words. From what I hear, JKR herself has talked about doing an encyclopedia of the HP Universe when she gets through all 7 books. If she decides not to, hey, I'm ready to go! :)" That he would try to ahead with publication knowing that she is preparing her own encyclopedia is odd, to say the least.

This is being reported as another story of the little guys standing up to the Big Bad Corporation, but those reports are ignoring a lot of the facts of the case. JKR and WB have allowed many, many other books to go forward either without challenge or after vetting the appearance and content of the book to ensure that it is obviously unauthorized.

(And yes, I'm a fan, but I'm an academic fan who is very concerned that I be allowed to use books, TV shows, movies, etc. in my own critical work, so I'm not thanking RDR Publishing and Steve Vander Ark right now for making it harder for the rest of us.)