The end-user is not the developer who re-uses GPL'd code, but the guy who uses the final program. By licensing code under the GPL, you grant the end-user the r

The end-user is not the developer who re-uses GPL'd code, but the guy who uses the final program. By licensing code under the GPL, you grant the end-user the right to use and modify any program using your code as he sees fit (as long as he adheres to the rules of the GPL on re-distribution), and no intermediate developer can legally take that right away. Of course this restricts the freedom of indermediate developers, but the GPL is intentionally -Ouser, not -Odeveloper. It just so happens that some users are also developers.