The GPL License modifies copyright. The Netscape case has nothing to do with copyright but deals with a very specific license. The "License" is a contract specifying specific conditions, points of law and jurisdiction. These points could not be known without reading this particular license.
Copyright can be a default because it is simple, well known, and national / international law. The creator of the work has all distribution rights and everyone else has none unless specifically given by the creator (except within the conditions of "fair use").
The GPL simply loosens copyright restrictions, so if you hven't read it, your presumption would be copyright applied and that would be well within the GPL.
Now if the GPL had a clause that said the jurisdiction for all disputes was the court of Boise, Idaho, then there must be informed consent to that condition, and the ruling in question here would apply to that condition. Distribution of GPL'd source would have to be much more formal.