The ASR definitely works, although on a dry road, straight line acceleration in a 159 doesn't usually create a wheelspin problem. The software on the 159 seems to allow a certain amount of wheelspin in any event. On a 2.4 the additional engine weight would make wheelspin even more unlikely.
On an icy driveway 2 years ago with ASR engaged my car wouldn't go anywhere - it sat there with the light flashing and the wheels slowly rotating and no amount of throttle changed this - the ASR over-rode the throttle. Mind you, with the ASR disengaged it didn't go anywhere either! lol
The VDC is a different kettle of fish - this is only disengaged with a sustained press of the button. This feature will brake single wheels under the influence of various accelerometers, speed and yaw sensors etc to keep the car under some semblance of control. I have felt this cut in on a couple of occasions - once when tanking round a roundabout and finding some slippery spilt diesel - there was a sense of a giants hand pulling the car back into line. It works.
As Jon156 has mentioned, the same system incorporates the Q2e electronic diff feature on cars from MY2008, which will brake the front inner spinning wheel when cornering hard, thus diverting drive to the outer and gripping wheel and force the car into the bend. This DOES work, albeit at only about 50% of the efficiency of a mechanical limited slip differential. There have been many discussions on what this does - with a number of noted disbelievers who think it is just a different name for anti-skid. The difference is that the ASR systems usually cut drive to the spinning wheel by limiting throttle input - the driven wheel gets no further drive until the spinning wheel drops its speed to that of the driving wheel. On the Q2e system, by braking the spinning wheel the torque is transferred to the driving wheel which gets MORE drive - increasing stability and driving the car into the corner, significantly reducing understeer.
The same system also provides the Hill Holder, by controlling the brakes in conjunction with throttle position and speed and torque sensors.
These systems pop up on more and more cars these days as they are standard features of Bosch ABS systems, so they are not unique to Alfa Romeo.