Do your players have their characters run away from fights?
If so, why?
If the PCs are essentially disposable, not-special, not-beautiful-and-unique-snowflake playing pieces, and the fodder by which GMs prove their willingness to play tough, why flee?
I read somewhere someone saying that OSR stood for "Oh shit, run!" - but does it? Why run? Especially at lower levels, you can just make up a new guy. At higher levels, you can get your guy fixed from anything short of "irrevocable death" and wishes will make that negotiable.
I think there are two opposing strains of thought here. One is the idea that the PCs are disposable. The other idea is that you should flee from tough encounters.
Maybe when players ram their hapless heroes into brutal fights just to see if they can pull it off, they aren't being tactically dense or foolish or playing the game incorrectly. They're showing a real understanding of what "your PC is disposable" means.
Running way shows you value the PC. You have your guy run away to live and fight another day. You have him tough it out and die a terrible death for the amusement of yourself and your friends at the table because you value the entertainment more than the PC. And isn't that what you're saying is the point in a high-lethality game?
I'm beginning to think the guys who have their imaginary guy fight to the death, or quaff that unknown potion, or push the big red button, have a good reason for it. The fun is the point, and if the PCs are disposable, they're just the means to the fun. Greg Costikyan's Paranoia RPG classically makes this the whole point of the game. But there is a reason that resonates - it's the logical extreme of a disposable hero game. Fleeing to fight another day is a good idea if you want to preserve your guy but it's not the message that character funnels, high-lethality play, unbalanced encounters, and TPK-as-common-event play sends.
If running has value, then PCs have value. They have to be "special" in some way to make it worth running away. If they're replaceable or easily fixable, then what is there to run from?
So yeah, maybe the guys who don't want to run have a point.
(Editing Later: I wrote a followup here: More on Disposable Heroes)