you seem to confuse the meaning of a fact, and a belief. you BELIEVE that Mercedes is giving you exactly as much power as they say they are. Fact is that they aren't. Same with BMW, Porsche, Audi... Most people on this forum know that. So either the whole world lives in a cave, or it's just you.
Check this graph out, posted by this alpha company. 541 WHP from an AWD automatic transmission. 20% loss from AWD set-up means 676hp at the crank. And don't tell me these numbers are inflated because why would a tuning company want to undermine their own business by saying a STOCK car has more power than stated? In fact most turning companies only post their own results and pretend their tune got a LOT more power than before. Oh btw look at the Motortrend test where they dyno'd their E63 S and again... 541hp at the wheel...
Then look at BMW.. 320i/328i quoted at 184PS 245PS
Dynoed at 181 and 242hp... at the wheel
it's not 100hp difference.. it's a percentage difference. welcome to Earth my friend.