I'm guessing Tesla gets to cheat a bit since they don't use heat engines and don't have to run a bunch of air over a giant mesh screen to keep the engine from burning up.
Also, that giant pane of smooth glass over the top probably helps.
They get to play on a tilted playing field. They do have to lug around the weight of the batteries, but for cruising at highway speed (where the aero figure is most important), extra weight matters little.
Also, that giant pane of smooth glass over the top probably helps.