I have to agree that this book was not necessary, but now she wrote it, she can't simply say "Well only 7 people will own the book, and no one else will read it." Because that would not be fair for the people, the fans that have supported her from the begining or at least have curiosity to find out what these stories that wizards have, but muggles don't.
And I also have to agree, that before reading it off the internet or something stupid which in the end will happen, I prefer to buy it (it may sound crazy but oh well XD)
And have any of you noticed how many books she wrote? 7? Coincidence? In the Deathly Hallows, in the dedication, she dedicated it to 7 people, (i dont know if the 6 books she had she gave to the people she dedicated). But she actually did 'give' one to the people who have stuck with Harry until the very end.
So hopefully (and if not I'll have to beg xd) she will publish it. :D