Why do some companies discount it? My guess is because time and phase correctness and first order crossovers place constraints on the drivers (must operate in much larger ranges) and this can lead to reducing the power handling and dynamics of the speakers.
How many times have you heard of a spica or dunlavy owner blowing a tweeter ... quite a few. My guess is that it's not unrelated to the coherency of the speakers. How many time aligned speakers produce good solid bass ?
I prefer accurate to loud so it's a trade-off I can live with. Plus by adding a powered sub I lose coherency only in the lower octaves, where it doesn't matter so much.
The other thought is that so many speakers are placed suboptimally for imaging (the principle benefit of coherent designs) that many owners will simply never appreciate it. I'd bet over 90% of high end speakers sold are never correctly placed in the room for optimal sound, due to ignorance, decor, WAF etc.
For example if you put my spicas close up to the rear wall they sound pretty awful ... so many buyers would assume they're bad speakers. B&Ws, Harbeths, and other non-coherent speakers would probably sound much much better in that placement, leading the buyer to assume (erroneously) that they were much better speakers.
I guess what I'm saying is that the market for coherent speakers is probably narrowly focued on hifi nerds like myself, who organise the room around the stereo, rather than vice-versa. You don't get to be the size of B&W by pandering to our needs.
