Yea, 'if' you have locked your car for the evening and the next morning, for whatever reason, you go to your smart and find that the car won't unlock due to a dead battery, how would you get into it to CHARGE THE BATTERY?
My guess is that in that scenario, the 'key hole' on the drivers side WILL UNLOCK the door, but NOT LOCK IT.
Guess the MB engineers didn't see a need for locking the car up with a dead, or no, battery. Maybe something they should rethink for 2010?