If something is important to a setting, it should be represented as such mechanically. Fluff is not a good way to represent theme.
For example, say you want a gritty military game. You can't use standard d20 mechanics and tell your players "but don't do anything that would get you killed in the real world, or it will kill you here".
As another example, if you want to run a game where magic is dark, mysterious and dangerous to your soul, don't use the standard D&D magic rules.
This might seem simple... but you'd be surprised how many games ignore this sort of stuff.
And some people might be philosophically opposed to the basic premise I'm operating under here, namely: crunch > fluff.
If you have a philosophical disagreement with this, tough. This is my law. Go write your own law. However, I think you'll find that setting attributes in crunch are much easier to apply and much easier for players to buy into because, you know, they actually affect the game world.
Telling players death could come at any time and to act appropriately is a hard sell if they can charge machine gun nests with little danger.