All-Wheel-Drive for better traction in poor conditions (Snow, Rain, mud, etc.). It is understood this may reduce range (due to weight and extra power needed), so it should always be an option for those who want it and are willing to pay for the extra costs.
A 2013 Audi A6 offers AWD as a $2200 option. AWD on an ICE car has little relation to the mechanics and design of an electric car, so competitive pricing may not be relevant.
As of 2021, all S/X/Y models are AWD as standard. The Model 3 is available in RWD and AWD styles.
A dual motor AWD option was first announced in October 2014 for delivery in December 2014 for the Model S.
… this is THE key feature I am waiting for to buy the Model S (Model X isn't an option because of other reasons) - hopefully implemented 2015?
I 'm living in a mountainous area (Alps) with potentially lot of snow in winter. I am used to an AWD car and would definitively miss this enormous improvement of traction - although the Model S is known to show more traction than an average car ;-)
This winter I've already had 2 episodes where the lack of all-wheel-drive has been painful. The car handles very, very well on packed snow or ice. However, if there's a small area of unplowed snow (such as in a parking lot after a snow storm and the plows have pushed little mounds of snow in front of all the parking rows), not having the front wheels contribute to getting over a little (or not so little) hump of 6-8 inch unpacked snow makes maneuvering very difficult and just getting across it uncertain. Believe me, AWD would be a huge bonus in places like the Northeast, and I know many, many people who would never consider a RWD car in this region. I would gladly put myself on a wait list right now to trade-in my P85 for a P85x or something like that. In addition, a smaller front electric motor could be set to a different gear ratio, to contribute to greater efficiency at different speeds, or better acceleration if appropriately geared.
Granted the Model S in its current configuration only drives the rear wheels, as does the Roadster. Yet, it may be premature to conclude that these vehicles drive like your average RWD ICE car. They don't. The difference in weight distribution makes a huge difference in handling, not only due to the often-cited unusually low center of gravity. It is at least as important to have the weight equally balanced between both axes, and to have the majority of the weight concentrated close the the car's pivot point (center). A sporty ICE car may have a low CG and close to balanced weight distribution, but unless it has a mid engine, the weight of the engine is far from the car's pivot point, usually over the front axle.
Which is all just theory to explain what you experience when actually driving the car in the snow. Don't judge before you tried. You may find that you don't need the added weight and cost of all-wheel drive. To get an idea, look for videos of the Roadster in the snow.