From Article 1 Section 8:
To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries;
We can debate what "useful Arts" means or what "limited Times" means, but that is unnecessary as Congress passed copyright laws very early and they are a well established part of American law.
What is amazing is that Vivendi Universal has shown that the marketplace can allow for the protection of IP while also allowing for fans of a given intellectual property to create new versions of existing IP. Vivendi Universal has decided to allow the fan created King's Quest IX to be created by the current fan only public creation team. According to the agreement, "Vivendi Universal Games (hereafter VUG) granted a fan license to Phoenix Online Studios to continue work on the KQIX project. As part of the negotiations between the two companies, VUG required a change of name of the project. As a result, "King's Quest IX: Every Cloak Has A Silver Lining" will now adopt a new name: "The Silver Lining"."
Mods, minor program modifications, have become somewhat the norm in the game fan community, but this marks a new high point for the industry and leaves open the possibility that companies may make available more IP which is financially not viable but has a loyal and talented fan base.