So, go to any Youtube clip from a TV show, and you will see comments consisting of nothing but random lines from said show. For no reason. People just type them in.
And, when you think about it, how else would Google figure out what was being said? Voice recognition is hard. Far cheaper, surely, to brainwash, or possibly genetically engineer (it tends to be mostly the younger users) millions into posting the words as comments?
I'd assume that the site ranking works in much the same way. No doubt those people have special tools to move pages up and down, Digg-style. The whole link spam thing, then, is clearly just a ruse. Bad, naughty Matt Cutts!