I don't know what the demographics are for play groups who run multiple campaigns in the same setting, but I'd guess they're pretty numerous. Bob's game deals with PCs saving the north, Michelle's deals with the South, etc.
That said, I would imagine that the default assumption is that each region can handle its average problems pretty well, but needs PCs for when things get beyond the NPC's capability to handle things. By reducing the average level of the NPC protectors, you let PCs be really vital a lot sooner. And of course, the arbiter of when things get beyond the NPC's capability to handle things is going to be the DM, so I'd guess it'd all work out pretty much the same way it does in largely any other campaign setting.