IIRC the 4x number officially came from an article in BikeBiz about 2 years ago but it is generally known in the industry. I do not believe it includes single speed backpedal brake hubs but I could be mistaken. At the time the most prevalent bicycle was a 3-speed which surprised me as I'd think a single speed backpedal would be most prevalent. Saying that they are rare because you've never seen one in the U.S. is like saying that you went to a local lake and didn't see any sand so sandy beaches don't exist.
BTW, for repairing a rear tyre. Best is to just loosen the tyre on one side and pull the tube out where it needs to be patched (without removing the wheel), patch it, stick it back in. Takes about 5 minutes total. Next is a removable rear triangle such as on many Workcycles. Third is probably to use a spreader to spread the stays enough to squeeze the old tube or tyre out and slide the new one in. Last option is to remove the wheel.