Well, opening up a level or simply browsing through visual resources in the editor for current EE show that a lot of stuff is specifically made for top-down view, if you look at most stuff, it can turn into nothing (invisible) depending on the angle you view it from.
True, and I seem to recall some spots of blackness did occasionally appear in certain areas right on the edge of the map in early releases of D:OS.
As much as I'd like to see distant lands from eye-level it'd be so much work to do; either that or create the hemmed-in feeling you often get from that sort of perspective.
I remember fiddling about with the settings of Sacred 2 to get (almost) over-the-shoulder perspective though I forget how that worked. Just distance fogging, IIRC. Actually I just remembered I have some screenshots, so it does this: