Sony has launched their own iOS reader. This will allow for users to read books purchased on Sony’s platform. It’s not very widely-used, but if anything it’s another option for consumers.
That said, it was widely publicized when Apple blocked Sony’s eBook app in the past. It had something to do with how the payment system works. Apple wanted 11 percent of the cut, but Sony tried a workaround that meant the user would be redirected to their iPad’s browser rather than make the purchase within the App. This meant that Apple did not get their cut. Apple felt it was fair since the app was featured and distributed on their platform. Guess Sony finally decided to play by the rules.