Because just since Player X can play on A and player Y on B, that does not mean it's guaranteed to happen. There are so many people at net cafes, it's very easy to have people in there that never played at the same time. By your logic, those must be smurfs - but of course they aren't, they just randomly never played at the same time. So detecting them as smurfs would be wrong. Ergo it is not as easy as you say it is. Same with the other situations where households don't have a game-ready PC for every person, that's very common. They'll never play at the same time but on the same PC/IP, thus they are smurfs?