Some nobody told Gates exactly how to get rich with computers. I read it (the specific advice) in an old issue of Dr. Dobbs Journal of Computer Calisthenics and Orthodontia. The key is that out of millions of people saying millions of things, Gates was the one to pick up on the important one.
So, sure, he was lucky in a way, to be around and read it, but it seems unfair to say he merely appropriated value that belonged to everyone. The advice was worthless to the person giving it away, and everyone else.