I believe that another significant reason why most touring bikes have mtb hubs is that they're better sealed than road hubs, which matters when you're on the road for a long time.
I'm of the opinion that dishing of a rear wheel has more of an influence on wheel strength than hub width. Stands to reason that you want equal "stretch" in the spokes on either side of the hub which is best achieved with equal tensioning of spokes either side. One of the reasons for running a Rohloff hub gear.
But then I'm no engineer either so.......