That's a weak argument. Sorry, but if they need those rules, they will easily be able to get ahold of them. Heck, you don't need the books. They can be explained in a few sentences! But the books will be available. There are MILLIONS of them.
Greyhawk is used as an EXAMPLE of what you get when you set out to BUILD A SETTING. It's AFTER the chapter on how to make your own, as a "You might wind up with something that looks like this" kind of way. It's only 30ish pages, and it does the job it set out to do.