As FaithRaven said, they are aware that there will be piracy, but they want to make sure to keep the amount down somewhat. As for the people talking about the second-hand market, it is true that there would be plenty bought that way, but I've known several people who pirate, and if they weren't able to pirate, they probably still wouldn't be able to hold off buying some games when they first come out.
Also, as others have said, when things sell in the second-hand market, it still removes that object from the stores. When the stores run out of the used copies, at least some of those people may buy a new one. Additionally, if they sell through the used and new copies, they will then have to try to order or get more copies (providing it is a game still in production). Sometimes for legacy systems, it is a bit more acceptable, but plenty of people pirate current systems.
