I see the truth in what you say, but after the car ages, or sensors change, or the engine wears in, etc, the MAP sensor will have to be adjusted accordingly.
Additionally, this fuel system was used on a number of other cars (Porsche, for example). Bosch may have made thousands of the sensors, assuming they would be adjusted by each manufacturer at the factory for the particular engine application.
and look at the 4.5 fuel system articles posted there. There are procedures for testing the MAP and other sensors, but this assumes you're a Mercedes-rated mechanic with a specific testing unit (such a thing might be available on eBay, come to think of it). Many of these tests can probably be accomplished with a multimeter.
Testing the MAP sensor windings will tell you whether the armature is good, but because there's a vacuum chamber within that may have leaked over time, the only way it can be calibrated or adjusted to maximize the car's performance is by use of a gas analyzer.
A couple years ago, I uploaded an article on what values to look for and how to adjust both the ECU and the MAP. One is adjusted based on hydrocarbons (the MAP, if memory serves) and the other with carbon monoxide emissions (ECU). The air valve adjusts the idle speed.