[snookca]

In addition to what everybody else said, there's also trying to find pirated material for niche markets. That is, it's hard to find. I sell an e-book as well, and have foregone any DRM.

More to your point, could people buy the book and give it to their friends for free? Absolutely. And I'm sure some people have. Again, I'm okay with this. I'd rather people bought the book but like print, I can't stop people from sharing and ultimately, I don't want to.