Hours?

In the United States, why do some people measure driving distance by time? As in, that place is an hour away?
>At what speed?
>In what kind of traffic?
There is a reason that cars don't have an hours per gallon rating.

In the United States, why is gasoline called gas?
>There are hundreds of gasses on Earth
>Gasoline is not a gas; it is a liquid

In Europe, why is gasoline called petrol?
>There are thousands of petroleum products on Earth

People, don't be lazy and save yourself saying a couple of extra letters. Say what you mean and mean what you say.