Most cars I have owned have had fuel economy within a similar range, that being high teens in city driving and low 20's in highway driving, starting with the BMW Bavaria in 1971. The improvements in technology have been mostly offset by increases in weight and power. This is particularly true for the big ski/family vehicles: 162hp 1991 Toyota Previa minivan, then 240hp 2002 Acura MDX and now 300hp 2011 Porsche Cayenne, all with similar fuel economy.
The 4 cylinder non-turbo cars, 1975 BMW 2002 and 1986 Honda Accord, did a little better, low 20's city and mid-20's highway. The V-6 in the 1995 Nissan Maxima gets similar mileage, which is impressive considering its power for its time and that it's stilling running at 280,000 miles.
The Tesla Model S uses 437 Wh/mi. That's 6.3 cents/mile with my average utility rate of 14.4 cents/kWh, about the cost of a gas car getting 50mpg.