The GPL allows all commercial use. It does not allow proprietary restrictions on redistribution, under certain circumstances, but that's different. You can charge as much money as you want for GPL'd software, and you can base your commercial service on GPL'd software, etc (by the way, this is not just hypothetical -- billions of dollars of commercial activity are based on GPL'd software, including but not limited to the Linux kernel). It's just that when someone receives a copy of GPL'd software from you, you can't place further restrictions on their redistribution -- the permission to redistribute under the GPL comes with the copies. Think of it this way: the GPL prevents monopoly, while permitting commercial use.