BTW, dividing damage by 10.000 for immunity even has a kind of 'simulationist' background: The idea was that a being like superman might be immune to bullets, shells, skyscrapers toppling on him, etc. - but if a being able to smash Earth with its fists starts pummeling him, he might feel the pain. Your acid experience was similar to what would happen to a fire lizard being thrown into the center of the sun. Yeah, you might be immune to heat... but maybe immunity only goes so far ;-)
Or in other words: There is always someone out there being able to get you. Never feel safe. It's ADOM.