Earlier quoted context omitted.
ABS is very simple and only needs to know the difference between the speed of the tire and the speed of the road. It is more complicated systems like ESC (which works with ABS) that need to know about steering inputs.
I thought the "speed of the road" was calculated by checking the speeds of the other types, which is trivial if you are going in a straight line, but needs correction if you are steering, hence needs steering angle? Or is there a simpler way in non-ESC systems?
I'd imagine once they are implementing ESC the ABS also gets the benefit of steering sensor but it is not strictly necessary.