Look, there is a problem with textbook prices and there is plenty of blame to go around. I am pretty sore about this topic, because I just had to turn in my book order this week and the publisher has come out with a new edition of my favorite textbook, only four years after the previous one!
I'm a history professor, and yes some of my colleagues do not take price into account when assigning textbooks. But I do. I try to cap the book budget at $100 for all my classes. If I can assign a cheaper book, I generally do. This takes a lot of time and it would make my life easier if I just picked a pre-packaged textbook and document reader set. This act of convenience on my part would easily cost the student 20-30% more than my current reading list. That said, I can see why people are mad at professors who don't take the time to think about the cost of class materials.
Publishers are capitalist bastards out to make money. Like the article in Slashdot and the NYTimes editorial said, the cycle of textbook revisions has accelerated. Publishers crank out glossy textbooks with worthless and vapid on-line features, which add needless costs and increase profit margins. The publishers do this because the Internet has made the used book market more efficient. As a result the publishers have more competition from used book wholesalers than in the past. So they resort to printing new versions with more throw away features like CD-ROMS and on-line study guides as fast as they can. This is the magic of the marketplace and no law requiring the ‘unbundling’ of course materials can change the fundamental logic at work.
Finally, some blame rests with the students. I teach classes that cover the last 200 years of European history. I could hand out a two or three page reading list of a dozen articles and books that are superior to the dull plodding summaries offered in most textbooks. Most of the common primary source documents are available on-line or in various document collections already owned by our university library. The students could read these materials by looking up the journal articles on-line and checking out the books from the library for free. But they don't. First of all, reading and synthesizing that information requires more time and hard work than just picking up a textbook. Second, they are eighteen years old and want the convenience of a textbook. (I have had students tell me this in course evaluations.)
I keep assigning textbooks, because, based on exams results, class discussions, and course evaluations, students seem to read the textbooks. If students are not interested in putting in the sweat equity to acquire knowledge through the library they should pay for the convenience of using a textbook. Under the present market system, the publishers dictate the price of convenience.