It's very dependent on which car and where you are. A Tesla (any model) is best because their charging network is very reliable. And in most major US cities there will be many of them. In cities far from interstate highways, not so much.
Now days in the UK & Europe you can use most of the Tesla superchargers with any car. That will soon be the case in the USA too, especially now that NACS is becoming the charging plug standard.
Opening a supercharger location up so that it can be used by all vehicles is probably just a software switch / config file change in Europe. Tesla doesn't need hundreds of staff to do it!
