If I were a developer then the way I see it
Selling game on from one person to another (like dmpoole mentioned above) is generating me no money while 10 people have played that game.
So as far as I am concerned that is lost revenue really (no different from if they'd pirated it). The fact that second hand is legal isn't important as at the end of they day I'm not getting any money from either.
sid
You may not make money from the 2nd hand sales, but whos to say they would buy the game anyway if there was no 2nd hand copy available? They may not buy the game at all at full cost. A good game, even one thats 2nd hand, will cause news to spread about it which will encourage people to buy the game. Pirating on the other hand does the same thing, but it doesnt always encourage people to buy the game, it sometimes just encourages people to pirate it.
So pirating and 2nd hand sales are NOT the same thing. People realy need to stop saying they are.