*FANBOY mode ON*
Lexus surely needs knee bags because it has hard plastic in the bottom of the dash, or a poorly engineered safety concept. MB doesn't need that, only in the SLR because of a lack of space...
*FANBOY mode OFF*
(The W204 can have knee bags on some markets I think.)
I remeber some Japanese car, maybe the Toyota Century, with Airbags in the back of the front seats for the rear passengers.

PWND Lexus!