I think it is a part of Merc heritage to use vacuum rather than electric. Also it makes one feel more 'posh' to watch the locks go down slowly with a decent sound rather than that sharp electric CLICK.

I must say though that there are electric actuators that also lock slowly without those yukky clicking sounds.

"The Japanese cars use the electric switches and they have never failed, at least for all the old Japanese cars that my friends and I have ever owned."

It happens that the electric motor inside the actuator burns out. Not causing fire, of course, but the wiring inside burns thru which makes the motor and thus the whole actuator unusable. Could be because of exposure to water inside the doors. Happens to window motors too every now and then.

"Also, when the vacuum stuff works, why on earth MB engineers wanted to design a gas flap that is unlocked whenever the driver door is unlocked. If the vacuum system fails or the flap actuator fails, the gas flap is always unlocked and exposed to malfeasance by good-for-nothing people."

The gas flap is spring operated. There is a spring on the rod that keeps the flap locked at all times. When you unlock the vacuum actuator pushes against the spring. Should there be no vacuum, due to leak for example, the spring keeps the flap locked. Then you have special access from the boot to pull the rod to unlock the flap should you need to refuel.

"Oh well, if someone asks me what is the thing that I hate most about MB cars, I would say it's the failure-prone (I would say "pathetic") vacuum power doors/trunk/gas flap etc..."

Yes, they get pathetic after years of use and are a real pain to track but once you renew them they work again.

Remember, Mercedes is just another car. Although more costly, the accessories will not outlast their projected age by a lot. You have a good car for those few years, after those few years care has to be taken of various parts, just like with another car. No manufacturer claims their car will be perfect after years of use without proper maintenance taken. Though, they would love us to believe that.