I imagine that if your average Tesla driver doesn't use the Supercharger network all the time; in other words that they can also charge at home on a sensible tariff, and maybe also charge at work sometimes, then paying to "propel" your electric steed (can't refer to it as "fueling", as the idiotic HMRC don't recognize electricity as a fuel) is still massively cheaper than using smelly old exploding dinosaur stuff in your PanzerWagen.
Plus, it doesn't knacker the planet like smelly old exploding dinosaur stuff.
Don't get me wrong, I'm terribly pleased to have been one of the last S customers to grab free Supercharging, but I see it as a bonus, nothing more.