Yes, I understand the purpose, but I can't figure out how this rotation is supposed to be able to occur. The inner face of the thrust washer bears against the inner ring of the bearing, which doesn't rotate relative to the stub axle.
The inner ring (the "cone") will slowly rotate on the spindle (known as "precessing", I believe) due to the action of the rollers rotating around it - it's a loose-ish fit on the shaft. If the washer is not tanged, it may well turn the nut if the split pin fails, either tightening it and destroying the bearing, or loosening it so the hub falls off. Make sure it cannot rotate.
