If there's no gritty campaign setting you can think of, then the definition isn't very useful. If it doesn't describe anything, what does it mean?
Not expecting it to help, I looked up the word at m-w.com and dictionary.com. dictionary.com is worse than useless, it has two definitions; essentially a gritty setting is one that's covered with a coarse granular substance, or one that is courageously persistent or plucky. m-w.com also had a third definition, having strong qualities of tough uncompromising realism <a gritty novel>. Tom's system might arguably give grit if this definition is applied. Assuming it's realistic that adventurer's stats tend to be average.
However, in terms of actual usage, I don't think any of these definitions explain gritty the way it's typically used to describe, say a D&D game (D&D by it's very nature can't be gritty if realism is used as a key component of the definition.)
I'd say words like tough and uncompromising certainly do apply, though. Verissimilitude; my catchword to mean realism without actual realism could substitute in for realism in the definition. A setting that is harsh, dark, PCs struggle against system's or enemies they have little hope of defeating -- those are settings that are gritty, and they better fit the dictionary definition, as well as (I believe, anyway) the "common" definition. Can it have a mechanical equivalent? Yes, if the mechanics are very forgiving and allow you to get away with things all the time without serious repurcussions, then they detract from grittiness. But it's really more about the tone and details of the setting itself.
CH or others may disagree with me, but I'd say Midnight and Dark Sun stand out as quintessentially gritty settings. However, they don't assume that in order to be gritty you have to have crocked characters. Using a bit of hyperbole, let me illustrate the point I'm trying to make.
Let's say there's a setting out there in which the main focus of the campaign is an invasion of flumphs. Since flumphs don't actually attack, and -- if anything -- are more of a nuisance than anything else, this setting will struggle to gain any street cred in terms of grittiness, even if the PCs don't have stats any higher than 10. For that matter, an array of 18,18,18,18,17,16 doesn't really have any effect on the setting either. For exhibit B, let's say there's a setting in which the world has been pulled screaming down into the pit of Hell and is now the 10th level of Baator. Pit fiends wander the streets at will torturing and killing anyone they find. The entire world is periodically drenched in acid rain, or burned by active volcanoes or lava flows. Fiendish ancient red dragons rule all of the countries, brutally surpressing any sign of resistance. This setting will struggle to be anything but gritty, even if all characters start out with perfect 18s in every stat.
That's why I say -- and yes, this is opinion, not objective fact -- that gritty and stats aren't directly correlated, or even correlated at all. To turn my own phrase, they're not even on the same graph.