snapsc - If I can chime in while we wait for ASVJerry, Ohm does not use Walsh drivers these days, but they do use the Walsh principle of bending wave propagation, in which the back of a cone driver radiates sound in a quasi-omni pattern. Getting this type of speaker voiced right requires, IMO, a different skill set than voicing other speaker types. A few are really good at it, including John Strohbeen at Ohm and German Physiks (which does use a Dicks Dipole Driver).
Part of the reason so few do this is, perhaps, marketing. Many consumers expect a bunch of forward facing drivers in a box. Many assume omni's can't image well (which is false, IME). And in the early days, true Walsh designs were, um, finicky about associated gear and had some reliability issues. And then there is the price. Ohm Walsh speakers are not expensive, and since Ohm doesn't sell a $75,000 Reference model, they don't get a lot of love from the audio press or high-end folks. Selling factory direct is a two-edged sword, too, which keeps prices low, but means there is no dealer network to talk up the brand. Just my 2 cents.