Originally Posted by AlanQS
"330i, 330d, 335i, 335d; in the same way as with a differential interlock, brake intervention takes place on the rear axle if the drive wheels spin severely, improving forward momentum even if the DSC is disabled."
From BMW themselves, Page 75 of the Driver's Manual.
Default position = DSC engaged - All safety functions available. On snow, as soon as the wheels slip you will lose engine power, which makes progress difficult.
Press DTC button briefly = DTC engaged / DSC Restricted - The safety functions are all still available, but they will not act as quickly. This allows some wheelspin on snow, without cutting engine power.
Press and hold DTC for 5 secs = DSC disabled. Directional and stability systems are no longer available (except for ABS).
The wording you are quoting from the manual is new and was not in earlier e90 manuals. It suggests that the ABS module will brake driven wheels under severe wheelspin (even with DSC de-activated) to try to replicate the actions of a locking differential.