I dunno... what would this be ?
I am a logical-consequences sort of DM. I frequently "pull punches" when the dice seem to be going against the PCs, and I have been known to fudge the HP of the monsters when the PCs are having too easy a time.
Most deaths in my campaigns have turned into total party kills.
I have run with three groups, and their experiences are dissimilar.
Group 1: Many deaths, 3-5 per year over 10 years.
Group 2: Some deaths, 3-5 in 6 months, a repeating pattern over 2 years.
Group 3: 0 deaths over 2 years (should count as 6 months, though - chat based game, very slow).
Some are because the PCs meta-game think. Group 2 members tell themselves, and each other, that I would not throw something at them that they could not handle. Despite the fact that I say, flat out, not to think that way because that is exactly what I would do.
Others are because the PCs have a win or die mentality (retreat is never considered). I think that Group 1 plays too many computer games ... they act like once they begin an encounter, it is win or die; and they often act like having a cleared some rooms, the opponents will not move back into them.