The genetic makeup of the Aussie breed is such that the last third of the tail is brittle and delicate, making it prone to breaking or splitting, which would cause a lot more pain and trauma for the dog than the process of tail docking.
That makes sense. I was looking at two of my dogs the other day with a thermal monocular and the hound/cur mix has a thick tail that was the same temperature color as the rest of his body (except his nose). The thinner tail of the Pit mix was cold as her nose through the thermal. No meat/circulation in there.
