On further consideration, my complaint wasn't my real/best argument, consider this a redirect to rwallace's response above :p

That said, I personally don't take 'many' as meaning 'most', but more in the sense of "a significant fraction", which may be as little as 1/5 and as much as 4/5. I'd be somewhat surprised if the number of old machines (5+ years old) in use wasn't in that range.

re: scaling, the Ubuntu folding team's wiki describes the approach.