Okay, here's my take on it. As you said, the Oghre and Maul are definately related. They are almost certainly not Oghre young or anysuch thing. However, I think you discarded the "neanderthal vs. humans" analogy all to fast.
The reasoning for this is thus: First it does say (AFAIK) that Trow commited the act of genocide. That means they destroyed the race completely. This means no surviving Oghres.
Second, 'modern man' and neanderthal man coexisted for a pretty long time until the more evolutionarily modern man exterminated his lesser brethren. If you look at Mauls vs. Oghres I think they're more likely a distinct predessesor race. It says in the manual that evolution did take place since the Trow watched the other races "evole," so it could be that the Maul are the weaker, smaller and less intelligent cousins of the Oghre. When the Trow enslaved the Oghre, they enslaved only the Oghre, not the random nomadic tribes of proto-Oghre living in the Steppes. When they exterminated them, they had no reason to turn their wrath towards the filthy pig-midgits living in caves off in some godforsaken eastern tundra.
As for the Oghre surviving and building great cities in the Steppes, I'd imagine that the Mauls just ran around for a thousand years, eating what they could. They were lured into joining SB simply because the Blid Steppes are so frikkin' cold and barren, that they've been subsistance living for ever. I'd do it too ;).
So in conclusion, I jus think that the whole Trow-didn't-kill-all-the-Oghres-but-were-ashamed-to-admit-it
thing is too improbable to be what happened, thus my theory of the two seperate races (and why they look alike). Oh, and the reason the Maul were never displaced is because Oghre were effecively removed from the picture, leaving them the undisputed masters of their "land." Also, nothing elvolves in a thousand years…
Ta.
-Disc
