The last thing "Big Publishing" wants is a challenge to their little (HUGE) monopoly on text books. I mean if authors start going "digital" on text books we don't need printers and shippers and paper mills and lumberjacks etc. AND when you wish to publish and updated version of a text book its just a little bit of editing and an upload. So that destroys the industry because all of the sudden most of the jobs in "Big Publishing" are the 21st Century equivalent of "Buggy Whip Manufacturers..."
This is all part of the big education bubble ready to burst. My sibling works with textbook authors - university professors who make more money cranking out new editions than they do on their day jobs. LOTS more money. The textbook industry will eventually go digital but don’t expect to see a drop in prices.
In my industry we run into a problem like this on the software side. Software tools for the work we do are custom-made and extremely expensive because there simply aren't enough buyers to make it worthwhile for anyone to create and market something "off the shelf."
Kill off the hard copy and the price might be 20% less. Margin is huge on these and it’s going into the pockets of the author, the university and the publisher. Seriously, calculate the cost on running out a couple hundred sets of 400 black and white copies, and throw in maybe sixteen color copies. Less than forty dollars a pop available to anybody at your neighborhood Kinko’s. Using dedicated book manufacturing equipment is going to cost less than that. Retail $120.00? Who’s pulling whose leg?
The university, the author and the publisher would likely make more money on an e-book, they’d show a small price decrease while taking even higher markup. The threat is in losing control over the content published via that channel.