[xtho]

"For a few years now, people have been expecting electronic textbooks to take off in a big way: They're cheaper than traditional textbooks"

Somebody never tried to get a site license for something that is worth its money. Electronic media are much too expensive for the education market (at least for universities etc.). A "traditional textbook" you can sell once you don't have a need for it any longer. The effective cost is less than the list price. I've also made the experience that electronic media usually lacks the depth of "traditional textbooks" unless it's the textbook put on the web.