The specific case here was the professor had a financial stake in new books being sold.

I do agree updated editions with new information could be important, but again when theres a financial incentive to sell new books, the obvious lean will be towards making new versions even if there is no new information.

Since the books can be required, they should be required to show proof they have substantially added to their edition or else relegate it to a minor revision (maybe adding sub-editions like 1.0, 1.1, 1.2; where you only need the first number to be current). Right now its a whole lot of, "Trust us you need this book and the only pre-owned versions are out of date".

As a side thought, this is the kind of thing that makes me wonder if they use the book costs to weed out those that will not allow themselves to be abused to that degree. This would leave only those who would conform to their leader/manager/teacher and are less likely to try to change the system.