little things that seam like they would make a miniscule difference are actually a big factor. For instance the 2010 equinox had a lot of aero work done. Changes like bringing the windshield out flush with the A-pillars and recessing the windshield wipers eliminate a lot of turbulance. In the equinox article they made these changes for fuel mileage and because a lot of people complained about wind noise in the cabin. I'm sure the underbody has a lot to do with it also for the z/gtr as others said.
In my mind all cars probably cavitate to some degree behind the wake of the front bumper acting like a plow through the air. I'd imagine its the little things like wipers and side mirrors that have the greatest effect on CD.
