Personally I agree that accurate 'relative' fuel quantity gauges would be preferable to the rubbish we currently tolerate. But if fuel is issued in litres (and, for those who still haven't learned to pronounce 'aluminium' correctly, that's LITRES not' 'liters'), then the conversion to other units should be simplified and standardised wherever possible.
Mph and statute miles really have no place in aviation any more. It took Uncle Spam a while to accept Celcius, so heaven knows how long it'll be before they finally stop the statute miles nonsense in aviation......