The reason MB engineers set up the climate control system to default to outside air was simple: SAFETY. Remember, this is the company that engineers its hoods to be springy so that unwary pedestrians will bounce off; the company that heats up windshield washer fluid so it doesn't freeze when it hits your windshield; puts sensors on its brake pads to warn us when brake pad material is getting thin . . .
For those of us in cold winter country, recirculating cabin air in the winter is a good way to almost instantly fog up one's windows. I've done it with a Honda I once owned, and almost every day in the winter see drivers with completely fogged-up windows.
My owner's manual tells me that the boys and girls in Stuttgart set it up so that you get recirculated air for 30 minutes after hitting the switch if ambient temp is above 45 degrees F, and only 5 minutes if temp < 45.
I think it's a really ELEGANT solution to human forgetfulness.