There is some sanity remaining in Germany and what they do is a safety factor. There are two reasons for this design.
First, is in case you lose a brake hose or some other important part, you still have 1/2
a system left to slow down and not crash!
Second, is because there are many standard shift cars in the world (not us) and the brake master cylinder reservoir is also used to supply fluid to the clutch master cylinder. They cut costs by using the same design for all cars as there is a port at the back of the reservoir to slip a hose on.
Now, you wouldn't want to lose all your brakes because of a faulty clutch slave cylinder, would you?
C280Sport, 300CE, 400E, 190/5.0