It's a convenience and mental thing. I am more likely to go on long tours/holidays with my S knowing it's free (and bragging about it), so the calculation doesn't really work out.
Supercharging just costs a few dollars, and is way cheaper than buying gas. You can still brag about it.
I live in a country where people brag about their 1200 Km per tank diesel cars and where diesel is very competitively priced, so free SC still makes a big difference.