I know of very few cars with multiple rotation speed sensors on the wheels (and the system has to know the rotation speed of each wheel if the system is to func

I know of very few cars with multiple rotation speed sensors on the wheels (and the system has to know the rotation speed of each wheel if the system is to function properly). So each sensor (and all the associated cabling, wire harnesses, etc) is a single point of failure. ABS systems are far from fail-proof...