the larger gap allows for a larger spark, thereby burning the fuel more completely, resulting in a smoother idle and a little more power. The reason MB didn't use the larger gap is probably due to operating tolerances. Can you imagine what would happen if mercedes started stalling out because of bad plug gaps? It would be disasterous to their reputation, and would be entirely possible if a car had a worn coil or perhaps sub-standard plugs were used. Big companies always have to be a little conservative with what they do, in order to make sure ALL of their cars run fine.