While I understand the logic, I'm just not sure that the argument that piracy occurs largely because there is no legitimate alternative (such as buying recordings of TV episodes immediately after they air) really encapsulates the majority of piracy. Despite MP3 buying services and online game distribution, piracy in these areas continues unabated...
I think that it just boils down to this: Given the choice between paying for something and getting it free with (what is percieved as) very little risk, the average person will choose not to pay. This really helps explain many anti-piracy groups' actions... Random lawsuits, Kazaa viruses etc are all aimed at increasing the percieved risk.
Note I said "explain" not "excuse"... I won't state my opinion on whether these scare tactics are legitimate.