Bull. They're going to have to pay for an amount of gas anyway.
They're purchasing them because they're either Bleeding Edgers, and/or they think they're actually saving the planet. How much coal does it take to charge the car?
Now, if there were more Nuke plants, windfarms and solar, it could be argued these cars are actually having an environmental impact. But the same people who buy these cars are (in my area, at least) also opposed to nukes and wind power (kills birds, ya know!) and sloar is just too damn expensive. So they are offsetting their 'carbon footprint' to the evil electric company.