Yes, there's the thing. In theory, if EVERYone who downloads would have otherwise bought a copy (doubtful) and taking their making available theory into account, if I get caught torrenting a movie, I should be liable for a little less than 2x the wholesale price of a digital download. That assumes a typical torrent ratio of 2.
I say a little less since they didn't incur any accounting overhead. Wholesale because that's the price they get from everyone who buys from them (for example, what Apple would pay them had I gone to iTunes).