I can only comment on what I see.
In Denver we have one tech shop. I have never been in it!

I do however know many of the instructors that work there, and even the owner. They teach both PADI, and GUE. They do sell BP/W's but they also sell jacket, and back inflate BC's.
The shop I certified in was starting to sell some tech gear last summer, mainly DiveRite. They did have some Backplates, and the Transpac, and Transplate BC's. I have not been at that shop in a while, but sales of the tech stuff seemed very slow based on a discussion with the Shane (owners son). Next time I am there, I would not be surprised to see the tech gear gone.
Most BP/W sales appear to be on the internet. I know and dive with a number of folks who use DSS. You won't find those in an LDS, as they are direct marketed to the public online. I use a Hammerhead, also online direct.
The vast majority of divers I see (minus Scubaboard events) are using jacket BC's, and you also see a lot of Zeagle (or I do). I was just on a live aboard in the Channel islands, and with the exception of one crew member, I was the ONLY diver using a BP/W. However the boat was full of drysuit divers. This boat may not have been typical as it was chartered by a N. CA dive shop, and many of those on board were using the same equipment (not rental).
My observations of divers in the US would support the facts presented that BP/W sales account for a very small percentage of the diving public.
I also talk to a lot of folks that purchase used gear. Let's face it, many take up diving, go on one trip, and then they have a baby, or loose interest, and sell their stuff.
My first BC was a Ranger (used), and I picked up my Stiletto from an out of business shop in Key West. My BP/W was purchased from numerous places in pieces. My reg was new off of ebay from an LDS buyout. I would not be surprised to learn that most of my gear is *off the grid so to speak*, and I have a bunch of gear!