Apple’s new in-app selling rules are in effect, requiring retailers to give Apple 30% of revenues from book sales.  As a result, Amazon, Kobo, Barnes & Noble, and Google Books have stopped selling books through their apps.  SONY’s app was rejected back in February for the same reasons.  There’s lots of news coverage, a few are linked below:

Kindle, Nook & Kobo Apple Apps No Longer Sell eBooks – GalleyCat

Amazon caves to Apple, drops Kindle’s in-app button – Computerworld

Sidestepping Apple: From Amazon to Condé, Companies Rethink Their App Strategies | Epicenter | Wired.com