I wonder why BMW is so reluctant to equip cars with a mechanical limited slip differential. It doesn't cost THAT much, and it has a lot of advantages when it comes to traction and handling. I feel that a lot of the potential in BMW's cars are lost in open differentials and runflat tires.
And if it is too expensive, they should at least offer LSD and regular tires as an (expensive) option, and let the customers pay for it.
Or maybe they fear that they will not sell M-cars if the true potential in the regular cars is shown.