That argument is irrelevant. The whole point of these SuperChargers is that they would be located along interstates to make long distance driving possible.
Obviously if you never go more than 20 miles from home, you will probably have no need of a SuperCharger.
The smartphone idea is a good one, but useful only if you have the flexibility to choose. If there's only one station within range, you're stuck with it.
Tesla has pushed hard early on to ramp up the number of charging stations as a sales incentive. As the construction rate trails off, and the number of cars increases, that's when the problems will start to crop up.
I guess we'll have to agree to disagree. I don't see Musk sitting on his hands and doing nothing about it if it becomes a problem. When you run the numbers, they are not that expensive to build. An article from a couple of years ago indicates that each SuperCharger site costs them between $100,000 and $175,000. (http://insideevs.com/tech-crunch-what-it-takes-to-be-a-tesla-supercharger-partner/)
SuperCharger access is currently a $2,000 option at the time of purchase and comes standard on the higher end trims. Although I'm sure there is plenty of profit built into that number, you could build a lot of SuperCharger sites if you allocated $2,000 per car. Last year they sold 31,000 Model S cars and I'd bet less than 10% lacked the option. This rough, back-of-a-napkin estimation puts it in the neighborhood of 400 stations that you could build with last year's sales.
But like I said, the biggest mitigating factor is that other types of fast chargers are being built as well. And unlike different grades of gasoline, all you need is an adapter in order to charge at a “foreign” charge station.
Once upon a time there were not too many gas pumps in the world, but that problem did not last long.