Apple has revised their App Store terms, now these apps cannot contain any links, like to send users to a web page to then make a purchase outside the i-app. All sales from within the i-app mean 30% to Apple.
Companies like Kobo and the Wall Street Journal have refused to accept the new terms, they now no longer sell content via their i-app. Also, Google has removed their book selling app, they have now put it back in the app-store but without the "buy" function, same for Amazon.
Apple's marketing techniques are just like those of crack dealers... .. . Now that so many people/companies have become captive of the i-App-store it's time to see how much they can squeeze out of it.