In a way, rules are the de facto laws of physics for an RPG world. Of course, it depends on how consistently those rules are applied. 5e encourages rulings over rules and DM empowerment, so the DM who makes many off the cuff rulings can really undermine the rule-as-laws-of-physic conceit, much the the consternation of players like Saelorn. It's a little like 4e, that way, in that in 4e rules, though clear and consistent, were decoupled from 'fluff.' Conversely, in the RAW-uber-alles zeitgiest of 3.x, rules were very much the laws of physics.
Only in comedy like Order of the Stick, and a few GMs who treated their worlds like OoTS.
Outside of that, people in (eg) Greyhawk could break bones and suffer lingering injuries, despite the lack of rules for it. RPG game rules are no more the physics of a world than any other sorts of
game rules. I don't think anyone claims the rules of Advanced Squad Leader are the
"Physics of the ASL world"; I'm not sure why this happens with RPGs - it never happened
before 3e D&D (& AFAIK no one has ever claimed the rules of Call of Cthulu were the
'physics of the CoC world'), so I think it must be something to do with the presentation of the 3e rules.