I know several people that use older PCs. Not all because they can't afford a newer one. They just find that the computer they have does what they want.
My uncle has an almost 10-12 year old laptop running Windows 2000. He just needs to surf the web and email. Up til last year, my mother had an 8 year old laptop. If you don't play the latest graphics demanding games or view video, you don't need anything made in the last 4 or 5 years. Plenty of people out there are still happliy chugging along on 1.x Ghz computers. Sometimes even less than that. For alot of people, "if it still does what I want, why upgrade. It works! "
Oh, I've also seen a few and heard of people around here that use even older computers.