> It should, because practically everywhere in the US does it wrong

Where do they do it differently? I've been in grocery stores across Western Europe, Asia and Latin America, and the only place I recall seeing the single entry queue was at a Trader Joe's in NYC

The Barnes & Noble Bookstore (at least the two or three I have been to in the past 10 years) has a single queue. Fry's Electronics did it that way. The self-pay corral at HEB (a huge Texas grocery chain) with about 14 check-out stations does it that way. The Academy Sporting Goods store near me does it that way. The Austin Bergstrom Airport security gates are that way.

I agree that many places have a queue for each registers, but the other way isn't entirely rare.