I believe you are correct. Ohms law, says that the resistance of the device in the circuit determines the current flow. For example, you can plug in a 1 Watt bulb on a 20 amp circuit, but if you put a 3000 Watt device on that same circuit the 20 amp breaker will trip.
The Supercharger and car must handshake before charging begins. Something like:
Model S: "Hey, someone plugged into me. Who plugged into me?
Supercharger: "Hi Tessie, it's me. Glen Allen, 3A. What's up?"
Model S: "Nuttin' much."
Supercharger: "Say Tessie, how much go-go-juice do you want right now?"
Model S: "Hmm. Let's start at 112 kW. I'll let you know when I need to ease back to 90 kW. I'm a little sore."
Supercharger: "Whatever you say, Tessie!"
With other manufacturer's cars, the conversation might be:
Nissan Leaf, v4.0: "Hey, someone plugged into me. Who plugged into me?
Supercharger: "Hi Leafy, it's me. Glen Allen, 3A. What's up?"
Nissan Leaf, v4.0: "Nuttin' much."
Supercharger: "Say Leafy, how much go-go-juice do you want right now?"
Nissan Leaf, v4.0: "Hmm. Let's start at 33 kW. I'll let you know when I need to ease back to 15 kW. I'm a little sore."
Supercharger: "Whatever you say, Leafy!"
- - - Updated - - -
Of course, this is assuming any other manufacturers jump on board. And I don't think they will. The gift has been offered, but I suspect they are to stubborn to accept it.
I'm beginning to think this will be the case too. Too much "pride" out there. Nissan might accept, MAYBE Mercedes, but I don't see others accepting at this point. We'll see I guess.