Why are Harbeth speakers expensive while its drivers are not.

All great points above. I can only add to what davt said about what the market wll pay (or bear). It would scare the hell out of me to be a speaker manufacturer in this day of countless manufacturers. Anyone can go out of business at any time. If a company such as Harbeth marked their product up 1000 %, I wouldn't hold it against them. It simply doesn't matter how much it costs If the public isn't willing to pay the retail price. If Harbeth believed they could sell 10000 speakers a year CONSISTENTLY, they would be willing to sell for a lot less. Another factor comes into play then; would they really want to see their speakers in BestBuy! Scary, scary, scary.

One further thought. I wouldn't expect a speaker manufacture to change out drivers overtime the driver company called to say they have a newer " better sounding " driver available. 
Further the speaker manufacture, Harbeth in this case would have to change the model or put a II after it to designate the change. 

Price is based on the perceived value of Harbeth speakers by customers and not by how much they really cost.

I recently finished building the Linkwitz design, LX minis, and put together the "cabinets" for about $200 by purchasing the flatpack from Madisound. The dipole designs are much easier to get right than the fancy boxes, and these also use an active crossover and seas drivers. The sound is certainly different than the Harbeths. The stereo imaging is about the best I have heard.  Seigfried  has certainly spent the time to improve on his earlier designs, and charges only $100 to allow you to reproduce them. Give them a listen  and a look on the internet.

I bought a pair of dealer demo P3’s around 6 mos ago. Started them off in my main room, driven by Croft phono Int, I bought for them shortly after. In that room I ran a Tsd-15, Amadeus, A23 SUT. They were clearly able to show the potential of that front end...very detailed, and spacious. I have heard people describe them as warm and fuzzy, but not IMHO. Then I chose to set them up in the bedroom, so I can enjoy them more often. Currently have the Croft and Sony PS1 on the top shelf of an Ikea Besta TV stand, which is about 22" high with legs. Stays well below the drivers, and allows them to image nicely. Very enjoyable, but a turntable is in the works. Also thinking about getting back in to digital, since it’s a bedroom system, and I don’t wake up to my cartridge spinning in the dead wax (-: Wonderful speakers!