"By contrast, all eBook apps from competing eBook stores — such as those from Amazon, Kobo, Barnes & Noble, and others — cannot offer an identical shopping experience. They are disallowed by Apple. Apple has demanded from each of its iBookstore competitors a 30% cut of any purchases made using Apple APIs for what is called “in-app purchasing.”"

Saying that Apple doesn't allow those publishers to sell books at all and then in the next sentence saying they do allow it doesn't help your argument.