I had this same issue, so i asked...
what happens is "high" end tires usually come with a red dot of paint or yellow, or both, marking the high point on the tire based on harmonics. what these guys do is then make sure this red dot on the tire lines up with the shrader valve on the wheel, which is the low harmonic point of the wheel. if there is no red dot, they use the yellow. and gets you an almost perfect balanced wheel.
But I had my guys balance the tire, and all of the sudden weights where needed... so in my opinion these guys are just getting lazy with the whole balance part, and figured out that if the dot system works just run with it.