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And I'm not sure it will. If anything, it is likely to increase revenue, same as Google Print. Someone who buys this lexicon will buy other Harry Potter stuff, most of it written by Rowling.
I actually bought books because of Google Print; I was searching for information, I found the book that contained it, and I ordered it online. The book was not available at the local bookstore - in fact, I would not have known to look for that particular book if it weren't for the search I did. So the publisher made money on that one.
Personally, I think that Rowling should be allowed to control her intellectual property - but this control comes with consequences. Her fans are free to make their own decisions as to whether to give her their money, too. If they find her behavior so outrageous that they won't want to give her their money, it's their choice. Personally, I make a point of boycotting artists who have ridiculously strict copyright policies.