I think it does makes sense to consider them as particular cases of a more general concept, after all. Grammatical rules and the rules of chess would be other instances, somewhere in between.
They are all regularities, but laws of physics are regularities that people notice (or try to notice), while legal laws and chess rules are regularities that people impose. (Grammar rules as linguists study them are more like physics; grammar rules as language teachers teach them are more like chess rules.)
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.