It hurts them sure.
As it also hurts every other business. The big difference between buying a used game and buying a used car (or clothes, etc.) is that games (and movies and books arguably) are pretty much 'one time' playthroughs. Sure, there is some replay value, but very few games without multiplayer give the owner too much incentive to hold on to the game after it's been beaten.
Yeah, maybe later I'll want to replay some of my old games, but maybe not. With cars and clothes, you use that stuff everyday and while you could have bought used clothes or a used car, the person you bought it from more than likely (since those are borderline necessities) went out and bought a new car or new clothes. So the manufacturer still has 2 sales for 2 items belonging to 2 people.