Even a damp road takes a hit (one would think that the slight drop in traction would help. I guess the tires suction to the road with a layer of water).
The only trouble I have with winter weather (at least regarding traction and road-going) remains my uphill, concrete driveway. Driving on snow and snow-covered ice just doesn't have much effect on the i-MiEV. You'll get the occasional reminder from the ASC that the roads are crap, but even if there's just a thread of grip, the i-MiEV behaves like you're on dry road, at least when driven sensibly. I heard the Tesla Roadster is the same way.
Black ice, on the other hand, there's not much you can do about that. I've been sideways on that without the car noticing