Earlier quoted context omitted.
The Fit's estimated top speed is 115. Applying logic to the problem I'd say it goes to 140 because it probably supports switching to km/h mode (e.g. if you need to drive through Canada) and 140 km/h = ~85 mph which as you say is probably the reasonable limit to take the vehicle
Most speedometers have a second ruler specifying the km/h speed. It would add a lot of unneeded complexity to change the speedometer's movement rate depending on mph vs. km/h: It's a lot easier to just use a different guideline on the existing dashboard.
I agree that either way it's easier to use a single speedometer with a different overlay.