You are assuming that some one using pirated software would have bought it.
I think pirates actually harm people who make free and cheap software, by using expensive "pirated" software instead. Had they not used the pirated software, they would possibly be using the free stuff and boosting the use of that free stuff. The big boys don't lose out, because they wouldn't have bought it in the first place.
As such, the high moral ground the big boys think they occupy is equally suspect.
IMHO, given the lack of large software houses going out of business actually due to piracy, I don't believe piracy has any real effect. All that is happening is that people are using the software, and the software houses remain profitable.
If I am ever yo believe in piracy losing business money, I want proper proof that the vast majority of people which pirated software on their machine would have paid for that software. I suspect not. I suspect that if there really was a way to stop piracy, many more people would use Linux and all it's alternatives for free. In that scenario, MS and co would really start losing money and market power.
Addition Edit:
Also, most people spend the money they have. If they did buy all the stuff they pirated, software, games, music, movies, etc, there would be another sector that lost out. For example, pirating Far Cry 3 instead of buying, means £40 (whatever) to spend on clothes, food, cinema, fuel, etc. Its the same money, there is no extra. It just goes to different places.