While you need a decent studio to create a decent music quality, writers can create good-looking PDFs on their computer.
If there is going to be an iTunes book store, publishers and bookstores will take the hit. An author could charge a bit more, and the audience would pay way less. It would be more convenient to buy the book (one can read the first chapter before buying, not something you do in a bookstore. Nor do you have to go there).