But the point is, some of us feel that visual effects such as the page turn animation in iBooks enhanced our enjoyment of content without getting in the way.
Also, if enhancement of content wasn't important, why bother with visual effects like Parallax and the new zooming in and out effect when entering and existing apps?
While I can understand that some appreciate these touches (e.g. page flipping), neither of your examples "enhance content" in any way.
Your app isn't going to go far if it isn't a pleasure to open and look at while you're using it....
I wasn't suggesting apps should be ugly and that design doesn't matter. In the specific case of books, the primary selling point is the convenience vs. physical books. Superfluous interface elements may be important to some but are by no means critical for most.