I don't think it's that they can't smell you. I have dogs that are trained to search for narcotics, and they can definitely smell things when cover scents, scent free sprays, carbon suits, etc.. are used. But it makes a difference as to whether they are actively looking for drugs (paying attention) or not. It may be that using smoke or diesel fumes, that the other odor is so strong that it makes the human odor seem like it isn't fresh? I don't know. I just think that using a few examples where a deer was seen downwind isn't very good evidence, since I've seen deer downwind and had them come close on occasion even when I smelled like a sweaty human. I wonder how many nice deer smelled the smoke and said, I'm oughta here. The hunters just didn't know, or see it happen. For now, I'll just stick to learning the area and hunting into the wind as much as possible. Does smoking work? I don't know, but I doubt it. I reserve the right to be wrong. And as far as the native americans doing it, well, they also did rain dances.
Beautiful buck, by the way, KentuckyTJ. I'd use any cover scent that you wanted for a crack at that.