All this talk of D3 in inferno (for the record I haven't tried it nor is this thread about D3 but game design) reminded me of a time when I thought Morrowind needed more difficulty and tried Oblivion on the hardest setting. In case anybody tried it the game was brutal, deciding how to attack monsters that could one shot me while needing 1000 hits to kill, the first few minutes was fun I don't really disagree, but once I figured it out, once it was obvious that the only way to win a single battle was to exploit the weak AI, pathfinding, terrain elevation and gambryo, the game became impossibly tedious, even for a diffcultyf.. like me.
Grind does not equal difficulty, the effort taken to solve a problem is what equals difficulty. Once the problem is solved the grind should go completely away, and a new problem should be introduced. That is where difficulty sliders fail, the problem never changes for anybody, just the amount of work needed to get through it, like forcing you to take a test without a calculator.