For books, if I torrent something and find I really like the author, I’m more inclined to pay for another book in the series of another book by the same author. Same concept as music. Physically having a book in your library is worth a cost.
For games, one may buy a sequel or another in the series or recommend the game to a friend who would then go and buy it. Steam and other game services make it much less attractive to torrent than to buy it at a discount. Achievements, social network aspect, and such make buying a game come with other intangible benefits.
For movies, same concept applies. If the movie is in a series and the new one comes out, one may be more inclined to pay for it or see it in theatres or recommend it to someone else who will pay for it.
Of course in these scenarios, it’s totally possible that none of this happens and the content is acquired for free and that’s it. But when you scale these possibilities up by larger numbers of people, the chances are much higher that additional revenue will be made in the long term as a result.
We also need to keep in mind that piracy has its own high barrier for entry. The majority of the population do not have the technical skills to be able to successfully pirate content so we need to remember that when we think about all of this, we’re looking at a relatively small subset of the population.