If you add up all the auxiliary stuff you need to power with electricity and round up generously, it's maybe 2000 watts load. The very best commercially available technology of today can run that load for 45 hours. So the impact of the auxiliary system load is marginal. That means it's only a concern if you're contemplating using close to the maximum range of your car. If you're traveling 15 miles each way in an 84 mile range Leaf, or 80 miles each way in a 250 mile range Tesla S, you don't really need to worry about running the heater and lights, even counting diminished battery capacity.
The average American spends 25 minutes each way commuting; even in NYC the average figure is 34.6. Even double or tripling that commute time due to bad weather and halfing the range due to cold, that's still easy for the Tesla. It's a bit of challenge for the Leaf with its 24 kwh battery and 84 mile range.
If the typical electric cars of ten years from now perform close to the high end of today, then the vast majority of people won't have to worry about cold weather's effect on range. But a sizable minority of Americans are what the US Census characterizes as "extreme commuters": people whose commute takes more than 90 minutes or fifty miles each way. Even at the low end of that spectrum cold weather range won't be an issue, but if you commute from Fargo to Bismarck ND every day it's safe to say you aren't going to be going electric any time soon.