I find it astonishing especially considering the clunkyness of the iPad, that it has any book sales at all. It is not good for books(pdf textbooks is a dream and Jobsy pushed a new standard based on fixed sized for obvious lock-in). The iPad mini is a lot better for books, but unlike its big brother is unattractive compared to the opposition (Android on Small tablets...Large Phones and ebooks), and it has nothing in the Phablet form factor.
The iPad has lost momentum already, even though the tablet market continues to grow. IDC's Latest figures http://www.businesswire.com/ne... How about you focusing on competing considering content seems to be a massive market as massive mark-ups don't work when they are not hidden in long term expensive contracts.
Really though we(here on slashdot...and the backrooms of Apple) should be talking about DRM free...Open format books, anything else is stupid for the underdog. It is what we want.