Amazon, Barnes & Noble, Google Books and Kobo have removed their links to web-based stores from the applications for the iPhones and iPads. In fact, Google Books has removed the whole application itself.
The booksellers removed their links in line with an edict issued earlier this year by Apple that demands all apps offering content for sale or subscription to do so through the App Store, and not through external links to the seller's web store. Moreover, following its usual money making policy Apple require a 30% commission from all such sales.