Professor: Next semester we're switching to a new edition of this textbook. Samantha: What? They put out a new edition just last year!
Now the students won't get a decent price for a resale! What did the publisher change???
Professor: Comma on page 54.
Sadly, this is how it often goes. It's a racket. Publishers make meaningless changes simply in order to force students to buy new books instead of used ones.
The good teachers are aware of this and will allow students to use the previous edition. Most teachers, however, aren't that good.