Our surveys have shown that only 49 percent of iPad owners read e-books on them, which suggests that although the iPad is a blockbuster device, it doesn’t necessarily lead to book reading for even a majority of its owners,” says James McQuivey, an analyst at Forrester Research. “And even when it does, what we know about the success of the Kindle store and app suggests that more Kindle books are being read on iPads than iBookstore books. And why not? If you’re a book lover and are predisposed to reading e-books, you are almost guaranteed to already be an Amazon customer and you are likely to continue that Amazon relationship on your iPad.
И ещё одна причина: iBookStore существует отдельно от AppStore, куда ходят все. Сделала бы Apple «всё-в-одном» — и всем было бы проще.