The explanation being that the tire and wheel companies marked their product accordingly such that the alignment of the dot and valve stem would insure that the high spot of wheel was matched to the low spot of the tire thereby keeping the radial runout of the assembly to a minimum. Common sense.
Question, how would the tire company know what wheel the tire was going on, in any given application, to know where the high spot of the wheel was? Steel? Aluminum? Magnesium?
If I remember from my training a billion years ago, it was a balance issue. Tire steel belts have joints and wheels have holes for valve stems which create a very slight imbalance on either assembly. Lining up the dot with the valve reduced that imbalance as much as possible.
Somewhere along the way, we were told that setting the beads, then allowing the air to escape to relax the tire, then reinflation to pressure, equalized the way the bead set on the rim. Something most tire shops won't do as it adds time to the job.
