The situation gets worse when considering the near racketeering many publishers engage in. I had a couple of professors who assigned us their own $100 textbooks, which of course had a new edition every year and while they wouldn't rely on it much in class, they'd make sure to include at least one question in the exams about something only mentioned in the textbook (without stating that that would happen).
This kind of textbook "abuse" was pretty crazy in undergrad. In comparison, my graduate level professors all either used very old textbooks and didn't really care about the edition or outright used free textbooks.
Some of our professors would give us a "translation key" between new and old editions of textbooks, so we could work with used ones. For example, which exercises are assigned (in new editions they rearrange the exercises, for no apparent reason but to make the old editions obsolete...).
This kind of textbook "abuse" was pretty crazy in undergrad. In comparison, my graduate level professors all either used very old textbooks and didn't really care about the edition or outright used free textbooks.