I was thinking of Veek as I was reading the article. <IANAL> But my understanding is that model codes can by protected by copyright, but that once they are adopted as law, they cannot be. On the other hand, lack of public access is due to the particular option DC chose - Municode.com has been around for at least twelve years. We used it as the reference for city employees when I worked in city government.

http://www.municode.com/Library

I would argue that if a "law" is not fully in the public domain, it is formally unconstitutionally vague. If the information within is legally a secret, something I cannot acquire without pursuing a commercial arrangement with a private party on a voluntary basis, then the courts cannot reasonably expect me to understand that information, and the legislature has failed to bind me to obey those rules in the eyes of the due process clause of the Constitution.

I don't see it as requiring a special prohibition of "copyrighting laws", it stems directly from the fact that 'not public domain' is a variably mitigated example of 'secret'.