I'm a college professor and I've never heard of these kickbacks except from people claiming that they exist. I select textbooks because they are what is available. I hate it when publishers change a few minor things and put out a new edition. I have three versions of the same book published within a four-year period and the fourth edition is coming out later this year. And they keep changing the order of the chapters so I have to change assignments, test questions, etc.
Granted, I don't mind keeping my courses up to date, but I think a new edition of a text book every 16-18 months is a bit much, especially when the editions are not compatible for things such as exercises and chapter ordering. I LIKE used textbooks. I would encourage my students to use them if I could, but it seems that the publishers are trying to kill the used-book market for textbooks.
I realize that things change rapidly in computer science, but I think they could slow down the update rate a little on these books without sacrificing much. The only thing worse is when a good textbook is NOT updated at all. One of my favorite texts is now horridly out of date, but there is no new edition on the horizon and I really can't find a better book for the subject. I've been forced to use two lesser books (which I also hate doing - I think you should have one textbook per class).
Sorry for the rant, but I want people to understand that the professors are just as frustrated by all of this as you are, except perhaps the ones who author the textbooks. The fact that I receive free "desk copies" of books does not eliminate my frustration. I know my students are still paying huge amounts of money for textbooks and there's only so much I can do about it. I'm trying to find open textbook alternatives, and I may have to take time to write one if I can't find one.