Posted by http://www.cultofmac.com/141476/you-must-sell-your-ibooks-in-the-ibookstore-and-apple-gets-a-30-cut/

Not only does Apple get a 30% cut of all iBooks sold in the iBookstore, but publishers aren’t allowed to sell their books anywhere else. If you make your book in iBooks Author, you must sell it in the iBookstore or give it away for free somewhere else. You can only make a profit under Apple’s control, and your iBook can be pulled from the store at Apple’s discretion or not even approved in the first place.