To me, "gritty" is more about realism in fantasy; hunger, disease, people trying to live and survive. I've played a fairly gritty D&D campaign before, so it doesn't need to be reflected in the system. What will the GM focus on?
Since we rely on the system to fill that role on Mu*s, I'd like to add Burning Wheel to what I consider as gritty. I don't think Dungeon World is gritty, though Apocalypse World is. AW doesn't have any "survival" rules, though if you read the book you know that if you're not playing up the post-apocalypse then you are playing wrong.
This can be handled by wikis and news files, for the bolder games that are willing to make a statement like "you are playing this wrong".
@magee101: "Friday Night Firefight" has been the name of the combat system since the original Cyberpunk (2013, of all things; how we saw the future as depressing and how unexpectedly depressing it came down to be).