Electronic media which can be duplicated infinitely is a relatively new thing, culturally speaking. This is a new concept, and as such, we need to take a moment to consider this outside traditional legal concepts, and give some thought to the social and economic implications of piracy, and the spirit of theft itself.
Suppose two people go to the supermarket. One purchases a very expensive bottle of champagne from their personal savings for a special event. The other manages to slip a bottle of the same champagne into their coat, and walk out of the store with it. The person paying still can enjoy the product they have, so nothing is denied them. Meanwhile, the thief enjoys both the product and their saved money, and the vinter of the Champagne has only received half of the money owed them for creating the product. The store, the vinter who made the product, and the individual who buys the product all come out behind, while the thief comes out ahead.
Say someone purchases an expensive, new copy of "Call of Duty 12: The Gunnening", while someone else pirates a copy of the same game which was leaked to a filesharing service. Both are allowed to enjoy the product and receive its benefits, but once again the pirate can do so without having given anything to the developer. The pirate once again comes out on top, because they can enjoy both the product in question and their unspent money, while both the developer and those who purchased it legally come up behind.
Software piracy is a new crime... never before have we been able to produce an exact copy of an existing product at no material cost. As such, it gives us cause to revise our idea of what "theft" actually is. I would say that, since both pirates and thieves are denying the creator compensation for their product, and leaving those who purchase products legally in a worse position than they (however minor), after stealing the product, I would say they are one and the same thing.