I have found the distance remaining varies on how I have been driving.
For example, yesterday it said 90 miles to empty as I got on the
freeway (I live about a mile from the freeway). After a few minutes
it was up to 110 miles to empty. So it seems to track your recent driving
habit to predict the number. I suspect this is the best way to go when you
have one or two gallons left and most people probably use this readout as
they get near an empty tank. When you have a full tank it is less precise
because the further into the future you try to predict the less accurate
your prediction will be (you could spend the next 5 days in city
driving or the next day on the highway -- the system has no way of
knowing this and the distance to empty would vary greatly between
the two conditions).