I can't offer you any explanation, except that the Mercedes engineers designed the engine and dip stick that way and I generally trust what they do--based on the rest of their engineering in the car.

For a DIYer, I think it's definitely easier and cleaner to suck it out (as opposed to jacking the car up, sliding under, getting oil all down your arm while pulling the plug, etc.), and maybe the MB garages find that true as well.

I also have an acquaintance who--about 10 years ago--had a McQuick-Lube type place change his oil. They apparently stripped the threads of the bolt in the pan but sort of snugged the bolt back in. He drove the car for about 15 miles before the idiot light went on, but the motor was ruined. It finally (after much fighting) cost McQuick-Lube about 3 grand. Wouldn't take too many of those before you quit messing with pan-bolts and go to sucking out the oil.

The other question is, what's a good logical reason for doing it the other way?