If the patches required are considered "critical" then they can be downloaded by all Windows users, whether or not the machine validates as "genuine."

Here's a bunch of info on the Genuine Advantage program from Wikipedia.

I imagine that most large scale (distribution) pirates of Windows are circumventing Genuine Advantage so that any and all MS updates can be downloaded. The bit about the "knockoffs" being the highest concentration source of all infections sounds like FUD to me. I'm sure a lot of PCs in the US running completely legitimate copies of Windows have been infected, because the population is generally slow.