Dashboards are user or factory configurable. Our Ford Focus had a button to change between L/100KM and MPG.
My friend's VW Bora's dashboard was OBDII configurable. The options were Japan/US/EU IIRC. Setting to US not only changed it to MPG scale, enabled the door-open beeps. :D
It's much more direct for car to measure consumption as L/100KM. However the conversion is done by the instrument cluster on the VW. We were connecting to the instrument cluster via CANBUS and changing the setting directly on it. Also the beeps were handled at the cluster, not at the central config.
My friend's VW Bora's dashboard was OBDII configurable. The options were Japan/US/EU IIRC. Setting to US not only changed it to MPG scale, enabled the door-open beeps. :D