If they do sell xboxes, they at least achieve better cashflow. Better cashflow means they can pay more quack coders to come up with crap like xp, and SP1. And they can tout bigger sales numbers, which in turn produce bigger numbers, because when you see something is selling well, you normally think it's good, and you feel like buying it as well.
If they don't sell them, then they're in the red, and running scared.
So even if you mod the xbox, you're still helping M$ stay alive. Games or no games.