I am pretty sure that when granny makes coffee herself at home, she makes it at least as hot as McDonalds serves it. Whistling kettles and all.
In a country of millions of people doing stuff, sometimes the stars align wrong for someone, and they get hurt. It doesn't have to, and in fact rarely is, someones "fault." It wasn't granny's "fault" that this one time she fumbled the lid and spilled coffee. Given enough tries, sooner or later anyone would, as it is a positive probability outcome. But neither is the probability of it happening large enough to say McDonald's was "at fault" of something. Stuff happens. Sometimes nice stuff, sometime less so. No need to feed a lawyer army either way.
It's the same silly obsession with finding who's "at fault" that underpins the enormously inefficient (except for, again, for lawyers) "at fault" car accident insurance schemes in place in most states. Despite most accidents and other mishaps being the result of all manners of complicated, best modeled as random, factors. None of which are a specific party's "fault."
But of course, there's the old adage about most people ending up in law school, do so because they couldn't hack math well enough to ever get into the complex systems classes....:)