If it's a popular game, cloud sharing won't be enough to stop people from buying it. Take CoD, for example: two people can't be playing the multiplayer on separate accounts at the same time. Nor can someone else from the sharing pool be playing the game. People want to be able to play games at their convenience, and sharing isn't a replacement for owning a game. Same thing with single-player games, too. Limiting sales of used games, on the other hand, will force players to buy new.