I've come to the conclusion that in fact it is about much more than combat: it's about overall playstyle. Combat is just a part of it.
Gritty is near one end of the rail, but I don't have a good term for the other end so 'sporty' will have to do for now.
If the characters are frequently fighting for survival, Bad Things happening to party members is an accepted fact of life, and the DM's not pulling any punches, that's gritty. If resources are often scarce and-or are difficult to recover, that's gritty. If the characters aren't always expected to be the 'heroes' and the game still works just fine if they're not, that's gritty. If the characters fit right in as normal inhabitants of the setting, that's gritty. If the players can't plan out their characters' life-paths ahead of time because adventuring will likely either kill the characters or drastically change them, that's gritty.
Flip side: if the characters rarely if ever have to worry about their own survival and-or Bad Things happening to them, and-or if the DM is pulling punches to keep characters alive (often in service to 'the story'), that's sporty. If resources are easy to recover or handwaved, that's sporty. If the characters have to be heroes for things to function, that's sporty. If the characters are noticeably different from others in the setting just because of their PC status, that's sporty. If the players can plan out their characters' life-paths during char-gen in the expectation that path will be walked in full, that's sporty.
And while each edition or system leans toward one or the other* of these, each individual table still ends up making what they want out of it. It's just sometimes easier if the system in use isn't fighting you too hard.
So, gritty vs [sporty]. That's my take for the day.
* - or even toward both at once, in different aspects - 2e was bad for this as it tried to build a sporty game on a gritty chassis and just ended up kinda confused.