FIrst, who even pays for PC games besides MMOs that need reg keys. :P
Piracy isn't as rampant in the PC world as many developers claim- especially when you consider that consoles also have piracy.

Services like Steam, Desura, Direct2Drive, etc have vastly increased the amount of legitimately purchased PC games- especially Steam, because they have sales and discounts all the time. I can't tell you how many games I've just randomly bought because they were heavily discounted on a steam sale. I've discovered a lot of good games this way, in fact.