It's not an easy case at all (and in fact, the court punts on the big-picture question, deciding the case instead on fair use). There are two separate issues: (1) "whether people subject to US laws must pay to know what the law is," and (2) whether a legislative body can deprive the private entity of copyright protection in a work by incorporating that work by reference into a law or regulation.

Answering "yes" to the first question does not resolve this case, where a legislative body incorporated a private entity's technical standard by reference, without the private entity abandoning copyright in that work. The question is, what happens now? Does the copyrighted work automatically become public domain (what public.resource.org argued)? Or does the copyright remain valid, but instead we find the legislative body in violation of its obligation to ensure public access to the law (and, perhaps, find the law invalid on that basis)?

It is not necessarily the case, as public.resource.org argued, that the requirement of public access automatically eliminates copyright in standards that have been incorporated by reference. It may instead create an affirmative obligation on the part of legislative bodies to enter into appropriate arrangements with the private entities that develop the standards.