Hmm, I think it might be safe to say that there's a
tendency for GGF and HHF to focus on different aspects of a world. I'm not sure what exactly... heck, I'm not even sure that one could decisively say that (this thing) is the province of Grim&Gritty, or (that thing) is mostly Heroic High Fantasy...
But for the sake of avoiding the "Well, there's an example here where what you're saying is flat-out wrong so you must be lying through your teeth! Worthless cur!" syndrome, can we assume that there are some things that tend to relate to one flavour moreso than the other?
For example, it seems to me that there's a tendency for GGF to focus more on the lower end of the social/political/economic strata... the street scum, the footpads, the forbidding cults who sacrifice pedestrians in the cellars next to the Constabulary. It's about low-level corruption, even popular corruption, where commoners act much in the way that only goblins are expected to... The PCs are charged, mainly, with surviving. Not even that, they are charged with living virtuously in a world where the "nice guy" truly finishes last. What's heroic is their perseverance in living a life that is completely opposed to what is expected, what is pragmatic. Truly, no good deed goes unpunished, but the Heroes continue...
For me, HHF tends to focus on the grander battles between the Radiant Knights of the Sun God and the Marauders of the God of Darkness (for example). The corruption is generally seen as being the realistic, but no less clichéd "Powerful, therefore corrupt" where demons, tyrants, or bureaucrats, are the main antagonists. It seems to me that the folk, as presented in HHF, are basically good, and are brutally repressed by the evil tyrant, or theocracy, or what-have-you. The PCs are not generally concerned with simply surviving, but living and acting in such a way that will change the world for the better. Doing good is overtly reinforced.
I dunno, hehe, I suppose like it has been said before, High Fantasy and Grim & Gritty are states of mind, not exactly things that can be given concrete examples of... Still, I thought throwing that out would help shed some light, hopefully, hehe

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