I doubt that highly Yannis, an equivelant S500 (W221) is 51/49 and weighs in at 1940kg SWB while the A8/S8 has ~57/43 front to rear bias. The C55 is 53/47 to 52/48 depending on the version BTW. Sometimes I wonder were you get your information, perhaps VAG propaganda land.
Although, you are totally right about most cars using the front rotars for most of the braking force; with the exception of some car makers such as Porsche (notably the 911).