[Porsche-O-Phile]

Red nailed it (again). The schit that comes out of the fuel pump (that used to be called "gasoline" way back when...) delivers FAR lower potential BTU/h per unit than the old fashioned gasoline used to. That's a big factor. Another is the fact that today's cars are heavy as heck - they're loaded down with all kinds of mandated emissions and safety crap that probably adds 500 pounds or more versus vehicles from years ago - and that's despite advances in body panel composition, etc. which are lighter.