Oh don't act like it's not true. Everything in 40k is so obscenely dark that it loses all its' meaning because you're totally expecting everything to be stuffty. It's still good, but to me it's more campy than serious. Like those Ciphas Cain novels seem like something I'd want to read.
Of course it is ridiculously dark
And, ahem, in this universe, "there is ONLY war"
Because in the millenium of the 40,000th mankind is pitted against countless abd endless armies of xenomorphic creatures. Of course its going to be incredibly dark :l