Lots of folks are diving into the most recent TPK that you talked about and published adventures and whatnot, but I'm curious about the broader across games and groups idea that you mention here. With the exception of Call of Cthulhu[*] it seems like the rest of these are games where the tactical wargame element is pronounced.
So I'm going to suggest that the "problem" might be that you might be much better at tactical skirmish wargaming than your player groups are. Which isn't a problem when you're playing a wargame but can be a problem when you're playing a combat heavy RPG where the players are either not interested in getting better at wargaming or not capable of getting better at wargaming no matter what they do. The balance of power in an RPG is heavily tilted towards the GM, so if the GM is also a better tactician than the players and doesn't do something to balance things out, you're going to pummel your players eventually.
Now some folks will suggest fudging dice rolls and wasting actions and what not, but if you are the kind of GM who doesn't normally do these things then they probably will feel off to you and at some point you'll stop doing them and then accidentally crush the players yet again. So I'd suggest instead handicapping yourself by "nerfing" the monsters. Reduce their HP by 10-20% and/or their damage by a similar amount. Give them a -1 to 2 penalty to hit. Lower their AC. Reduce their movement. Remove a particularly powerful special ability entirely. Etc. Basically do some things to make the combat part of the game more challenging for
you.
Don't think of it as going easy on the players and "fudging" things though - down that path lies self recrimination and a belief that you're playing the game wrong if you don't go all out on them. Think of it as leveling the playing field to give them the game that the devs tried to build. There isn't a game with tactical combat in it that can handle a mismatch in skill level between the GM and the players when it's the GM that is the tactician in the group. And none of them really even try - I think they assume a general equality around the table (and honestly when things aren't roughly even I'm usually in the opposite camp where one player on the other side can outclass me tactically - which is easier to deal with).
[*] TPKs in Call of Cthulhu are only a problem if they're boring. I usually call a CoC TPK a "good way to end a campaign" if they're suitably dramatic.
EDIT: And
@payn basically said what I said except in a single sentence. Good job me...