Because it's the most aerodynamic body style so far, as for gas mileage goes. Look at the Chevrolet Volt it also resembles the same body style but with a small trunk: http://www.gotbroken.com/wp-content/uploads/2009/05/2011-chevrolet-volt-picture-4-588x441.jpg It's a plug-in hybrid from Chevrolet that's supposed to get over 230 mpg and will be on sale later this year.