ABS allows you to take maximum advantage of the traction you do have, but it doesn't magically improve your traction. The problem the GP is referencing is that

ABS allows you to take maximum advantage of the traction you do have, but it doesn't magically improve your traction. The problem the GP is referencing is that the driver (be it human or computer) operates the vehicle using some sort of model for the maximum available traction. (Some) Humans are able to notice when it is snowing, re-tune their model and drive at an appropriate speed. It doesn't seem impossible that some heuristic could be invented to do the same for a computer driver, but I don't think anyone has demonstrated that heuristic yet.