In approximately 8 years I have seen 3 editions of the same text book. The page numbers change and maybe a few questions are different, but for the most part, the text is unchanged from edition to edition.
The book companies do this to make money. New editions make old books obsolete and kids can't sell the books they own. Everyone is forced to buy new ones. But, not my students I assign work by sections and encourage them to buy older, cheaper editions which are just as good. I wish someone had told me this when I went to college. I'm thrilled when one of my students tells me she got a book for $17. So many never buy the books because of the price. And now, at least for some of my students, that is not a problem.
(picture from Grounds for Sculpture--Princeton, NJ--a great place to visit.)