I graduated from college with the distinct impression that there are two types of college professors.
The real ones: Those that don’t mind you buying/using 3 year old used textbooks, and
The institutionalized ones: Those that will fail you if you haven’t purchased the latest version of the same textbook.
I could say that if I was studying quantam mechanics or fiber-optic research I might need the latest and greatest. But for subjects that are directly derived from Principia Mathematica and the like, 1999 vs. 2002 versions don’t matter, do they?!