Even if you don't use the heater, cold weather reduces the effectiveness of the chemical reactions needed for a battery to supply power, causing the battery to drain faster (sometimes substantially so) and the Tesla is all battery.

Now, those electrical engines, electrical though they may be, still don't have 100% efficiency. I don't know how many kW the Tesla engine is putting out, but even at 90% efficiency you still have 10% of all that power wasted as heat. That's a lot of heat. Maybe it could be used for heating?

I have driven a Tesla Roadster for 3 years. The heater does not impact range much.

I suspect the hit is less for a hybrid, because in a regular Prius, the battery is basically used as a buffer, not a giant energy store. I have a plug-in Prius and my "pure EV" range (this is how far you can go without firing up the gas engine at all) is significantly shortened by cold weather. I haven't done any obsessive tracking of it and I've only been through one winter, but I'd say it's somewhere around 25% reduced capacity in the winter.

Winter gasoline is 2-8% less efficient than the summer blend. My Prius's mpg, that I've never reset since buying the car, goes down slightly in winter, and back up when the switch the fuel back, only by a few mpg, and less now as it's averaged over many more miles. Now at 49.1 (uk gallons)

Indeed, in a regular 2008 gasoline car, I notice a 0.2 liters per hour drop in idle power consumption if the AC compressor is off.

Hybrids do not store energy for the journey in the batteries, they store it in the fuel.

The storage capacity of the fuel is not affected (much) by temperature.

From a simple perspective, the batteries in a hybrid just serve to smooth out the energy demand and provide regenerative braking.

Not as much as the fact that the journalist in question simply didn't charge it.

Yes, that is exactly what the problem was, though it got lost in the drama.

The car has a protection mechanism to prevent the battery from freezing, and when left over night in the cold without a charger, it will actually run an auxiliary heater to keep the battery warm enough.

The reviewer expected the charge to be the same in the morning, so he called their technical support when it was so low. They didn't explain that the charge can substantially decrease overnight when parked in the cold, because it automatically runs a heater for the battery. Instead they suggested that it was an erroneous reading, and that it would correct once the battery heated up.

It wasn't really a design flaw so much as a mistake from technical support exacerbated by an overbearing response attacking a journalist for not being omniscient.