Are you sure they were 4WD and in 4WD? Were both a front and a back tire spinning?
AWD in the MO engages the rear axle when it detects slip on the front axle. In other words, it engages 4WD when needed. One of the systems, forget which one (TCS?), will detect wheel spin and lightly engage brakes.
Most 4WDs are engaged by the driver. I can only say that spinning the wheels isn't helping, it's actually worse. A case of the operator engaged 4WD and hammered the throttle. See
this thread. Slow moving with light brake pressure is the way to go, acts like limited slip. Static friction is higher than dynamic.
On another note, I had a chance to play - abondoned parking lot. These tires don't seem to be very good in the snow, but then the MO is 4000lbs. VDC does work and it cuts in really fast, but it feels like it cuts in slow due to the slippery conditions and momentum - physics, plus it's hard to watch the Slip light and drive at the same time. VDC monitors your steering wheel direction. So, when you yaw (g sensors), VDC cuts in but can't correct the motion immediately due to loss of friction and momentum, you turn the steering wheel to compensate and VDC backs off. What VDC does not do is turn the steering wheel. So if you think it will turn the steering wheel for you to compensate your yaw, it don't. What it does is apply appropriate brake pressure and throttle the engine back to regain friction - contact of tires with the ground. Trying to regain static friction. You still have to point the steering wheel in the right direction to regain control.
As always, let me caveat for the 1000th time, VDC won't correct everything, it has it's limits, you can overpower it IE do something so wrong that not even VDC can save you. But it does help tremendously. And, none of this stuff helps you stop any shorter.
A side note about ABS and EBD. First time I felt it work. It will stop you shorter than not having it. But you still have to plan way ahead and leave a lot of room and go slow in slippery conditions. I could feel it kick in pulsating the brakes and it seemed to pulsate on individual wheels/axles. Will have to relook the system descriptions.