ASC reduces power till slippage stops. However without LSD this will occur sooner than with LSD as only one wheel (in corners) is providing traction...so logically with both wheels driving ASC won;t need to happen...where I get lost is that in order for LSD to work sllippage must occur where one wheel is going at a speed 20% different than the other and this can;t happen as ASC would fire up...on balance you're probably right to be confused, it's just a way BMW screwed money out of people I guess. However remember that you can turn ASC off and have real fun using only the LSD (diff not drugs ...)