I am taking a guess here... since A class is so small and sitting close to
the ground, the room for suspension and driveline has become very limited.
Coil spring whether strut or normal B-type takes up alot of space... so leaf
spring or torsion bar is used.
Torsion bar is nice but again fighting for limited space may not be suitable
for A class... therefore leaf spring is used for this situation.
Now, parabolic leaf spring... I am not sure what that is but perhaps a new
way of utilizing leaf spring design with MB ingenuity.
Again for rigid rear axle... it is cheaper to use than normal MB setup and
takes alot less space in the chassis area.