The whole gritty/grimdark trend is the fault of lazy writing. A good author can create fear and tension with a few choice words. Poor writing relies on graphic description to get the point across. It become 'and then' writing, which is rubbish. Authors used to rely on the readers' intelligence and imagination to fill in any gaps. Now they treat us like we're ten year-olds.
Readers have to take some blame too, though. If you aren't willing to look at a dictionary once in a while then you will certainly need to have things spoon fed to you.
I think this is incredibly dismissive. Not all grimdark and gritty stuff IS about the lowest common denominator. Some is, sure. But the best is generally delievered by excellent writers who use the graphic nature of SOME of the genre and apply great writing to it. I get really irked at this notion that it's easy to write grit and grimness. It's not. It requires skill in characterization, in storytelling, in pace.
In other words the same skills any writer needs. And sure, like any genre, there will be a share of lazy writers. And, as with any genre, there's plenty of talented writers. I don't think anyone reading Martin and Abercrombie, for instance, would accuse them of having a weak vocabulary.
It may not be to your taste, but dismissing a whole genre as lazy and treating readers as ten year olds (though I do wonder where Lewis and Dahl stand in that analogy) is, to my mind, a pretty lazy argument.