In my experience DND has a very thin edge where the good experience exists. Outside of that its quite variable.

I cant comment on Warhams but other RPG's I have played dont really care about encounter difficulty. And I am not even talking about narrative only stuff. But even savage worlds I can go and find 10 wild cards or 20 wild cards or come up with almost any Ace, and its just a matter of player approach as to whether the encounter is difficult or simply deadly. To really create a TPK situation you would need to design enemies specifically to do that.