Your comment gives the impression that GPL is a set of restrictions that developers are unfairly enforcing upon others. In fact it is the complete opposite: it is a set of permissions granted by the developer which otherwise would probably be forbidden by law.
There is no "probably" about it. Law definitely forbids basically everything that GPL allows, that's why GPL exists: to grant those rights. And of course one would then expect the thankful user to at least honor the same terms. Nothing odd about that to me.
