Human beings can't even always tell what is faked or paid shilling, should we really expect Google to do better than human beings?
Gaming the system seems to be a constant in nature. Species all over the animal kingdom develop mimicry, camouflage, and other techniques to fool predators, prey, and mates. Black hat SEOs are just the digital equivalent of the mimic octopus (http://www.youtube.com/watch?v=t-LTWFnGmeg)
The Web is an ecosystem. You can expect Google to evolve overtime to respond to cheaters, but you can also expect the cheaters to constantly involve new ways to game the system. There's no foolproof algorithm.