Thank you for all your responses; they have been very helpful. And I'm not assuming any of them as legal advice.
So to be clear, no other creator of a useful origami model has ever asked before if their model is protected be copyright law, nor has he or she tried to register the model as his or her creation in a copyright office? On a related note, I think that it's quite unfair what the web page of the U.S. Copyright Office, regarding useful articles, implies; but that's just what I think : )
