I wouldn't be surprised if that last part was true. With my electricity costs, I pay about 4 cents per mile. If that's typical, and if the average Tesla driver does 1,000 miles/month with 10% on Superchargers (which I think is vaguely close to the truth) then the electricity costs would be something like $4/month/car.
There is a rumor their cellular costs far exceed their Supercharger electricity costs.