I see that there's a view that books prepared with Apple's iBooks Author software are not taking full advantage of the possibilities for interactivity. In fact, it is easy to understand why that might be the case - it is simply extremely expensive and time-consuming to take advantage of the features. For years now, publishers have been loading a good part of the production process on to authors by demanding photo-ready copy in computer files and cutting down on in-house staff to increase profits. No doubt many readers will have noticed one effect of this - a significant rise in uncorrected errors and typos in texts. Most publisher will simply not have the kind of multidisciplinary (and multimedia) team to take advantage quickly of Apple's new offering.
I can see the use of interactivity in school textbooks - and probably also at undergraduate level - but there will be many kinds of book for which interactivity would probably be a time-consuming and little used add-on to the text. Trying to squeeze in multimedia and interactivity when all the reader needs to do is to read, would be a waste of time.