A pirated copy demonstrates a wish for the product but does not neccessarily demonstrate a real market with a real demand for it at that price point.
For example, if you look globally, there are huge populations that have the capability to play pirated games but (a) can't consider $20 as affordable; and (b) can't use western payment infrastructures such as credit card payments.
If you look locally, a person who would play World of Goo for free but if offered it at $20 would choose some other entertainment - that's not a potential customer, that's shouldn't be counted in demand.
When I investigated a micropayments startup (we wanted to try it in our country), we found some surprising facts - a huge % of the world's population don't have access to banking systems, even if they DO have some disposable money and want to pay for online games - non-cc alternatives to buying Facebook currency and such were huge requests when we did our customer research.
I don’t know about you, but for €15, I could enjoy 10 hours of films in a cinema and back then™ when I was playing and buying games, I got a few months out of a single game (Pharaoh and Caesar III come to mind). 2$/h is definitely not a ‘fair price’ for a game I have to run on my own computer.
For the few who consider DRM to be a moral issue or to those who use DRM as an excuse to pirate harder or distribute - but in reality, unobtrusive levels of DRM like those used for DVDs prevent the masses from making near free copies of movies to distribute to friends and relatives.
All of them bought a bunch of kid movie DVDs legally. All of them don't buy legal DVDs anymore as they are a bad quality product compared to downloaded movies:
1) The original discs get scratched quickly and they don't know how to back them up (as they are allowed by law but disallowed by DRM) - if the kids ask to "repair the movie" it is simpler for them to download & burn a fresh copy of the movie they bought, rather than try to break the DRM (again, breaking the DRM is explicitly legal here).
2) The original DVD's contain unskippable ads before the movie. It's defective by design - especially if you want to limit your kids exposure to that brainwashing. Pirated DVDs provide a better viewing experience.
So, a lot of people who would be perfectly willing to pay $$$ for many, many movies got hurt by the substandard product. If the content providers had legally sold the 'piratebay-style' DVDs at the same price, they would get their money.
DRM hurts sales of many products. If one more extra customer pays for your movie because the DRM-free service is better, then it outweighs a billion of freeloaders.