Based on my experience in school you're right about the first point (though they are still churned out very frequently) but incorrect about the second point (at least at the school I go to- I suspect it varies from school to school). Professors frequently require the latest edition of a book. Sometimes you can use the old book, but oftentimes it makes it very difficult to do the homework as the chapter/problem numbers get scrambled around in every edition and new problems can be added in the new editions.