I know a guy who self-publishes a magazine---on paper. When he first started out, he lost money due to printing costs. But then the popularity of his work increased and he started making some profit. That's when some wiseguy decided to buy a copy, cut it up, scan it and then post it on some warez site for others to enjoy---without paying for it. Now this happens with every issue. He talked with a lawyer but they told him not to waste his money. This kind of thing is hosted on anonymous overseas servers and there's no chance of trying to stop it, or recover damages. He's still publishing and his sales have increased but I can guarantee you he doesn't think it's because his friendly neighborhood pirate has contributed to his popularity.
Here's the thing about this argument, and I have heard it so many times before, you cannot prove that the people who pirated the item in question would have bought the item if they had not pirated it. You cannot. While some would no doubt have done so, others would not.
So, while it's not a justification, the work in question is exposed to more people, some of whom will pay for the item after being exposed to it through piracy. If they never intended to pay in the first place, the existence or lack of piracy would have zero bearing on them. If they were going to pay and pirated instead, and then didn't pay in the future and only pirated, that is a lost sale, however, there is no way to prove how much of a percentage this actually represents. It could be as low as 5% or as high as 95% but there is truly no way to answer it.
This is where I find the largest fault with the MPAA and RIAA. They assume that every download represents a lost sale. I disagree. I cannot count the number of shows and/or movies that I have only looked at because I could download it and try it out. And, again, if I like it, I buy it. It's a filter that allows me to find the things I like, test out some new content to see if it appeals to me, and disregard the things that don't.
Radiohead released an album as donationware. Was one of their highest selling albums ever. The concept that we should be forced to pay for content before we know if it's something we would enjoy, is dying and well it should. If you want me to buy your stuff, make stuff worth buying, and not something you shit out while snorting a line of coke, drinking and driving through Beverly Hills.