I am running on stock Yoko tires, so I agree that they won't provide optimal traction on ice. After some reading, I found that stopping distance on ice can be 10x of dry pavement so I do realize it's hard to stop on ice.
My interest is know what is the expected behavior of the ABS/VDC on the '12 impreza. I know that ABS probably would not have helped in my situation. I allowed for 2x stopping distance, but didn't allow for 10x.
I would have expected that ABS to kick in the moment my car started sliding.
Since that didn't happen, I thought maybe the VDC over-rided the ABS to prevent possible spin out.
Or could it be that my brake disc had a layer of ice on it and the pad/disc itself was sliding not the tire? I had only driven the car for about 1min at this point, and this was the first time I was applying brake outside of parking lot.
Essentially, I got out of the the parking lot and the 1st red light that was just 1 block away is when my impreza failed to stop. I did slow down from 20mph to about 5mph.