Good point. Though even cheap modern cards have a decent amount of horsepower - the main cost-cutting is shared memory, which doesn't play much of a role in mining. I can mine close to 1/10th of a coin (on Slush's pool) overnight on my laptop; multiply that by a few thousand, accounting for only gaming time, and it's a not-insignificant source of income without even getting very large. 1 block / 50 coins are worth a few hundred US$ right now, and it's entirely passive on the receiving end.