But there's lots of other ways books can be done in a digital format. For one really excellent example look at Inkling [1]. Now that's revolutionizing a medium (in this case textbooks).
I can get behind Inkling being revolutionary because it seems to me (focusing on their Social Learning feature) that it is closer to Vannevar Bush's vision of the memex. It is like the memex[1] in that it is taking advantage of the interactivity and social capabilities of current tech to create an interface that better matches the way we learn. The way we learn indirectly from others via books (where information is frozen and up to you to learn from it) and the way we directly learn from each other (mainly communicating about a topic in a conversational manner).