True on the two parts you mentioned and add to that one aspect of cold air is it is harder to move out of the way.
Also some guys in NJ who took early delivery of the Volt tried some no-heater driving in lower ambient temperature and no snow in late 2010 when the first units came out and still got < 35 miles (summer up our way is 45 miles+). Since gm-volt has old threads going way-back to 2007, we should have some of those discussions here. Part of it may be using battery power to heat the liquid coolant to a point where it helps raise the temperature enough to bring the cells up to best temperature at 70*F within the pack.
The ambient temperature helps to lower the chemical reaction enough to make the batteries less efficient even if the heater isn't employed. I do want to find out how the Tesla's do in say "high-winter in Colorado in snowy conditions", or my hometown around Buffalo, NY. Or, even worse - up in Calgary or other parts of Alberta, Quebec, Montreal, and other spots where hydro keeps electric costs down and EVs have a bright future.
If A123's new EXT chemistry does as it promises, this kind of drop in AER may be less in future-designed systems in EVs. I doubt GM goes to A123 for the Volt but maybe in some other EREV or BEV that they build, they would try it. EXT is not going into the Spark EV in 2013.