I won't argue your point about the added safety of ABS in certain unusualy winter conditions as I know that it's nice when working at those specific times BUT IMHO, the odds of the ABS control unit failing at any given moment like that are very rare. It's more likely that the ABS and Tracs lights will come on the moment you start your car some morning and that will give you plenty of time to realize that your ABS system will not function on that day.
We also have black ice here but that in itself hasn't caused me any problems in my older, pre-ABS cars to date as I've driven through many winters and know when the roads are worse than usual.
ABS or not, the main item for good winter safety is having good tires (preferably 4 good snow tires) and you'ld be surprized how often I see FWD Volvos with balding tires in the winter months here. ABS/Tracs can't help a car with bad tires on ice or snow.