Originally Posted by Antifriction

I must say I'm bemused by the concern for precision. The spreading amounts to 1/5 of an inch - in a system where the wheel is mounted by eyeballing for straightness, then clamping with a friction device. I end up adjusting the lateral position of my brakes - because the wheel has moved enough to cause dragging, a matter of millimeters - as often as not after putting the wheel on. If that level of imprecision mattered, we'd be screwing locator bolts through axle-mounted ears into holes on the dropouts - and getting engine-type tolerances.

Symmetry isn't the only benefit of the axle method - it also loads in a very controlled way with a perfectly-aligned force that engages an intended load-bearing face.