I love LISNews for such things as pointing out this wonderful summary of the Harry Potter decision by Chris Meadows. It all came down to the fact that the Lexicon copied or paraphrased too much, including almost all of the two small books that Rowling wrote on Quidditch and magical creatures.
The decision does not prevent another lexicon or any other reference book. It clearly states (according to Meadows, I don't have time right now to read the original) that Rowling cannot ban reference books on the topic of Harry Potter to protect sales of her own future encyclopedia. She can only protect her original works from being overly copied.
The NPR story can be found here, but I haven't had a chance to listen to it yet.
Finally, a satisfying explaination.