I hope that digital books become a standard soon. The biggest advantage of my app is that you can't share it.
I wonder also what is the advantage of writing an app instead of using ePUB format and releasing it as ebook.
The digital books have been around for several years now. There are quite a few Lula members who have been publishing photography ebooks rather than creating an app.
As far as I know, the Kindle books use DRM technology to prevent copying (I don't know about iTunes / Apple format).