One of the things that made me fall in love with 3rd edition was this fact that PCs and monsters worked by the same rules. The Dungeon Master's Guide gave me the rules I needed to stat out cities and countries, and all the NPCs within, and it all made sense. There was a working economy, in the sense that towns had GP limits.
It's true though, that when I was playing with generating those towns and those highest-level NPCs, and how many commoners and experts were in the town, I wasn't really playing D&D. My players never fought the NPCs, and so I never needed those stats. But I believed that made my world more real to me.
So maybe what I'd ask for from a new edition, is fairly simple stats for actual play, but the modular ability to expand as needed, and therefore to be able to explain and simulate the entire world as much as I want to. I suppose it doesn't need to be in the core DMG, but what else are you going to put in the DMG? Is there even going to be a DMG this time around? Someone should start a thread about that.