A person has a song on her computer hard drive. She clicks on the song and plays it. No one is getting paid. The same person pays iTunes $25 for iMatch. She now clicks on the same song and plays it through her iMatch service. Copyright holders get paid.
Same action, same song, one makes money for the copyright holder, and one does not. This is found money that the copyright holders would never have gotten otherwise.
„Copyright holders“, wohlgemerkt, nicht „Künstler“.