The reason why the doors need a good healthy push is not because the doors are too light or too heavy, or because of structure for crashing, or the moons alignment with Saturn and Planet X.
It's because modern cars, especially luxury and near-luxury models have become much quieter over the decades. Seals are better, and HVAC systems uses filters to bring fresh air in only through certain areas.
That means that the interior is pretty well sealed to the outside when all doors and windows are closed. It's too help keep things quiet and sealed.
So, when you push to close the door, air is being pushed into the car/cabin.
Since the interior is so well sealed that incoming air creates pressure inside the cabin, and with no where to EASILY escape, the pressure pushes back and the door may not close fully if you didn't use enough force.
Fix: Push harder on the door when closing it.
TEST: Open your drivers window and now shut your door. Notice how much easier it closes? If you use the same heavy force as when closing the door with all windows and doors closed, it may now sound like you just SLAMMED the door shut. That's cause the windows open and there is a space for the air to go.
If you latches are misaligned you should hear a harsh sound like a "bang".
If you have that take it to your dealer to have it fixed.
In the olden days when more metal and weight was though to protect one better, doors on Mercedes or higher end cars were heavy. So when you push to close them they would slam with a solid thud. But, in those days the cabins were not as sealed as they are now and the air had plenty of places to go and escape through.
The modern sealed design is better as it helps keep the interior quieter, and provides better climate control when you're inside.
Don't fret, rejoice, and enjoy!
