The right analogy is that a lock has been designed which any number of keys can be made to fit, but only a small number fit by default. If we require that users can always make additional keys fit, then we get the benefits of DRM (you know only authorized keys will fit) with the benefits of the GPL (anyone can run what they want on their own machine).
That said, I think Linus is right. Managing this for end users is complicated. In practice people will either not modify keys at all, or will bypass DRM by allowing a key that everyone can use.
Cheers,
Ben