How do you think it is going to work on cars with tech? Do you realize how much processing power it would take from the ECU of the nav to constantly be tracking distance, mileage, and elevation from current location to the nearest charger? Personally, I -highly- doubt that a car with nav/tech package is going to work any different. I guarantee you (I'd bet my mortgage on it) that ALL cars, even those with tech/nav, are using "as the crow flies" distances from your location to the nearest charge point. This would be the fastest/easiest (and lowest amount of processing power) required to constantly keep tabs on distances.
I'm sure Tesla accounts for this by factoring in some sort of percentage. Meaning, if your car has X rated miles left to empty, and you reach a point of maybe 110% of X, that is when it warns you. Allowing for 10% of "added" consumption when you travel to that charger. It seems like they would have to allow for this, because of too many variables (weather, traffic, HVAC usage, etc) that would prove way too difficult to attempt to calculate on the fly. My two cents on this matter...