Doh, that`s what you were on about! Funny I didn`t realize that, I actually filed a bug report on the issue about a year ago

Well, that problem can come up with any lighting, UE2 or not, it seems to be some sort of bug with DS lighting.
I didn`t see any of it on the Easy Environment sets with my default lightings.
I didn`t see it on the quick UE2 test run I did before either (
https://dl.dropbox.com/u/38361004/Screenshots/WinterUE2.jpg ), but now that I know what to look for, I can see a tiny bit of it on the terrain, the skybox seems 100% clean.
As for non-UE2 lighting, my "trick" to avoid it is using a proper set of directional lights for ambience. The EE sets are built that way, with one sunlight and 3 ambient lights. It goes well with landscapes imo.
I believe when using UE2 it`s more or less a gamble.
Anyway, good thing you care a lot about good lighting, imo it can easily make or break a render.
On a sidenote, the promo renders are 100% untouched, there is not even any brightness or contrast correction, so the lighting you see there is exactly what you`d get for Poser & DS.
On another sidenote, "Winter" got released, they just hide it well...
Link: Winter Daz Store