Far as I know, in a 140-chassis car, there are no connections under the hood for a jump start.

On my car ('92 300SE) the mechanism to release the shifter from park isn't electrical, it's mechanical. If you can get a key into the ignition, turn it to the 1st click, press the brake pedal and shift the car from park.

I have no clear answer as to why MB chose vaccuum for the door lock system, but I know that they've been at it a long time. My dad had a '75 280 and it had vaccuum locks, but there was no pump like in my car. There was a reservoir in the trunk that stored engine vaccuum and that supply was good for several actuations of the locks with the car off. After the vaccuum was exhausted, you could still get the doors open, but the central locking feature was gone until you started the car again.

In the 140 chassis cars, there are tons of things that are run off the vaccuum/pressure system. Door locks, rear headrest retractors, lumbar supports, reversing aid masts (only on 92/93 cars, I think), trunk lid handle, trunk closing assist (only used to help extend the retractor pawl), manifold vaccuum assist for the ventilation system, trunk release. I'd guess that the pump that does all that draws far less electricity than separate electrical devices would to do all those jobs.