Cory Doctorow answers this question:
Full answer at: Little Brother » About this book/FAQ
For me -- for pretty much every writer -- the big problem isn't piracy, it's obscurity (thanks to Tim O'Reilly for this great aphorism). Of all the people who failed to buy this book today, the majority did so because they never heard of it, not because someone gave them a free copy. Mega-hit best-sellers in science fiction sell half a million copies -- in a world where 175,000 attend the San Diego Comic Con alone, you've got to figure that most of the people who "like science fiction" (and related geeky stuff like comics, games, Linux, and so on) just don't really buy books. I'm more interested in getting more of that wider audience into the tent than making sure that everyone who's in the tent bought a ticket to be there.
Full answer at: Little Brother » About this book/FAQ