[Porsche-O-Phile]

The most aerodynamic shape is a teardrop with the blunt end forward - having a big vertical drop-off at the back end is actuall one of the WORST things that one can do aerodynamically. Tons of drag created by that profile. Likely driven by govt mandated bumper heights, taillight requirements and market demand for visibility, higher-up seating to make vehicles easier for phat 'mercans to git in and out of, and increased trunk capacity to fit all their made-in-China crap they're shuttlin home from Wal-mart.

There is NO aerodynamic benefit to having a squared-off back end. Although if you live in one of the many areas where you spend 90% of your time stuck in traffic never going above 20 mph then perhaps it doesn't matter...