Because students won't be able to buy used textbooks anymore.
Why are the schools going along? Presumably, the price to students will be kept reasonably low, at least enough to make up for the lack of cheap used books. Since the publishers (and authors) don't make money on resold used books, that's a new income stream to them, and they ought to respond by making the new copies cheaper.
(By the way, I've downloaded the new iBooks Author app and have started throwing together an experimental project to see how things flow. It seems pretty intuitive so far. I like the way you can easily toss in photos. If it works, the idea is to upload it to iTunes, and perhaps charge some piddling amount for it.)