Purpose built touring bikes have always occupied a very small section of the total bike market and by the early 80's very few manufacturers even offered a touring bike in their lineup... this has been the mainstay of more than a few small builders for quite some time as the market was not supplying what people wanted.
Surly has done a good job with the LHT and Trek's 520 is a pretty nice off the peg touring bike... the Miyata 600 and 1000 pretty much held the fort for quite some time.
There used to be quite a few frame builders here and all but one focussed on building racing bikes and mountain bikes and those guys are gone while we continue to make touring bikes as the demand has been rather steady for the past 30 years.
And people tour on pretty much everything, adapting what they already like and making it better.
I agree that most stock wheel sets are sub par for extreme duty and in the case of the LHT, it seems that more people use these for all round transportation more than they do full on touring and Surly can drop their price by offering less expensive wheels that will handle this kind of duty.
Some of the bikes we build get custom built wheels and depending on the use and build requirement, a wheel set might cost $600.00... we have put 48 spoke tandem wheels under some touring bikes that have heavier riders who also carry a ton of gear.
My touring bike is a refitted Kuwahara Cascade and it has no lack of braking power, can run some very wide tyres, has a beautiful ride, and has taken me 10's of thousands of km in absolute comfort. My build cost was pretty low and being able to do all the work and build wheels helps with that.
It is one water bottle mount short of being perfect and I will take care of that.
Conversely... we also build these which cost many times more than my Kuwahara... disc brakes are getting to be a pretty common feature although this bike stops just fine with v brakes.