I know it's not the brakes, but you only need the DSC to fail whilst you've got your foot down going around a corner, and be trusting the DSC to do its job, and "hey presto" the back end steps out and your in a ditch! (or worse).
I'm sorry, but I think that it could be safety critical in certain circumstances, just like the Prius brakes if you are gently braking (but not hard braking when the brakes are good).
I have to say that I am a bit dissapointed in BMW - there are loads of BMW Service Information Bulletins (SIBs) on DSC faults and yet they fail to acknowldege there is a problem.