Don't like the S-Class, fine. The Mazda 6, Lexus LS, Audi A6/ VW Passat, Infinity G35, and many others all rate in the same ballpark as the Prius in terms of coefficient of drag.
I would tend to agree with the basic point you're making... I think the Prius's exterior styling has in part to do with achieving a low Cd, but also ends up being sensible packaging for the goals of the car -- the five seats, the amount of cabin space, the amount of trunk/storage space, and room for the batteries, without needing excessive space.
As for the examples you provided though, it's clear that there are more options. The Fusion, which body-wise is quite similar to the 6, as we've discussed above, did manage to slot in at #2 on the current fuel economy list, without sacrificing its appearance (although I think it's less pretty than either the first, lovely if basic, Mazda6 or the second, gorgeous but way too big Mazda6). The articles so far indicate that numerous minor changes were made to improve the Cd, but clearly the car looks grossly similar.
