I have to disagree to an extent. Back in the day there was a d20 Cthulhu book which we used to run a game. It was quite successful, in the sense that most of the PCs died or went insane by the end (level 6 or 7), and we all had fun.
Admittedly, it was a mod of D&D with a much shallower power curve. If you took the D&D classes and just dropped them in the Cthulhu mythos setting, you might end up with very different results.
If the players and DM buy in to the premise, I think with the right modifications D&D can accomplish most things quite successfully. My group has run all kinds of crazy games using modded variants of D&D (from modern supernatural investigators to sci-fi settings where we played as alien invaders with incredibly powerful personal force fields). I won't go so far as to say other games can't do it better (while I've never had a chance to play them, I've heard great things about Dread and I really like the Gumshoe system as well) but D&D can be perfectly functional with the right tweaks and proper mindset.