[tshaddox]

> Producing a DVD is cheap, the seller can produce them for almost nothing per unit (not zero though).

That's true, although I was thinking more about retailers who presumably pay much more than the marginal cost (though still much less than the retail price). It's also probably true that copyright laws are responsible for the vast majority of the commercial value of physical copies of digital media. Perhaps an easier way to see the fundamental difference is that when you're downloading a copy of a movie from BitTorrent, all the parties actively involved are willing participants.

> It could be that this stolen DVD allows N people to discover its content and buy the DVD.

This is also a real possibility, and is a strong argument for copyright holders to rethink their business models (and, in my view, for societies to rethink copyright laws). But I don't think it's a strong argument for treating the theft of a physical DVD and someone torrenting a movie as being remotely comparable.

[gridspy]

It is possible that movie (DVD, Blueray) sales are similar to book sales. The stock is only paid for when it is actually sold. That allows shops to hold huge stock on day 1 with less financial risk and also to price-match all other shops regardless on when they received their stocks.