> Only the owners of a copyright have standing to sue

That's not true, at least in some countries. For example, see this case in France from 2009:

http://arstechnica.com/information-technology/2009/09/big-gp...

> "We've long said the GNU GPL is enforceable, and of course we're pleased to see another court reaffirm that fact," said FSF France president Loic Dachary in a statement. "It's a commonly held belief that only the copyright holder of a work can enforce the license's terms—but that's not true in France. People who received software under the GNU GPL can also request compliance, since the license grants them rights from the authors."