Instead of greed, might the cost of textbooks be high because - demand is low? How many copies of a text on applying Berner distributions to switching theory going to sell? (yes, that is gibberish). But it has to be made worth the publisher's investment to print it.
On the other hand, the people who write these books, usually college professors, deserve to be paid too. Although publishing textbooks is probably a good investment in their careers, so they may not need to make as many dollars from a book as the publishers do.
Here's an interesting thought: With the price of publishing reduced, will more textbooks become available? Or will we just get flooded with worthless, uninformative, poorly-written textbooks?