Speed of the wheels ??!! .... why?
I believe that for most normal cars: the speed is measured from the final drive gear output shaft.
As for the ABS sensor, its unique and only function is to measure / DETECT and to allow for comparison between the vehicle "global" speed VS. the wheels speed.
In the case the wheel is no longer moving, BUT the car is still traveling, ABS is then engaged when brake is needed (to prevent wheel locking)
You cannot use the wheel speed to allow both function as to measure the speed of the car AND the speed wheels... How would you know when you need to stop or advance...
just my 2 cents