Not sure that's true. Low drag is incredibly important to the top speeds of those cars. For example a `03 Golf has a CdA of 6.89[1] while a new Ferrari 458 is 0.330[2]. Also, most modern supercars have active aerodynamics to create more downforce at higher speed.
[1]http://ecomodder.com/wiki/index.php/Vehicle_Coefficient_of_D...
[2]http://www.autozine.org/Archive/Ferrari/old/458.html