Uh, I think you took my post far too literally. Obviously the DM can screw up or screw the players. But in general, I think most DMs try to be fair, and I don't think it's really that hard or that big a deal.To give the absurd form of the argument:
If the GM puts Tiamat on the first level of the dungeon and allows 1st level characters to walk into it without warning, their death pretty much is on the GM's shoulders.
Now, maybe you personally are so fantastically good that you never over-challenge without telegraphing it. But as a generalization, GMs cannot (and should not) outright disavow culpability. The GM is part of the process, and some of the responsibility can thus fall on them.