There are several issues here:
1. Companies such as NAD, Bryston have a reputation that they have worked hard to maintain. Irrespective of the Class they use, I am sure they will spend a lot in terms of optimizing the product as well as matching each amp to their signature sound. Of course, quality is also there.
2. These companies spend a lot on advertisement, marketing, participating in exhibitions, etc. That costs a lot of money and is amortized to the product cost.
3. Their reputation also means they have to maintain spares and service network and ensure the product is repaired and returned to the user ASAP.
4. Irrespective of how old their product is, I am sure they maintain circuit diagrams and BOM of all their products. For example, just a few days ago I wrote to Hsu Research on a hum that my VTF-2 started giving. Within a few minutes, they write back to me as to what to do exactly. With part number and location in the circuit!
5. Again, irrespective of the Class, these companies do a lot of research into sound and how it is to be delivered. For example, IC manufacturers such as TI, ST and others provide the complete circuit diagram for an amplifier based on their chip. They also provide fully populated boards as prototypes. Companies such as NAD may certainly look at it, but they will never use that circuit. They will find ways of improving in every part of the circuit.
6. These companies have a certain size that they find comfort in terms of selling. So they will never use an external power unit as companies such as Lepai do. They would rather design their own and build it as part of their over product design. A Lepai, on the other hand, would use cost cutting to the max extent possible without losing quality.
All these steps cost money, and when we buy a product, we pay a part of these costs.
Now begs the question. Why would a user spend, say, 1000$ for a reputed brand's Class D amplifier, when they can get the same sound, wattage and specifications for $100? Ego? 'Oh, I will never tarnish my sound system with these here today and gone tomorrow products'? That is human nature when it comes to what we love. We would like to show off what we have, not what we hear!! Even if the show off is to ourselves.
I still remember when I lugged my Hsu VTF2 from the US. When I reached Chennai customs, the customs officer asked me what it was. I told him it was a sub-woofer for my HT. He looks at the name, tuts tuts, and whispers in my ear. 'Next time don't buy such trash. Get a Sony!'. Since I was so ill-informed about sub-woofers, he shooed me out with asking for any duty. Poor me!!
The good part for us at least is that some of the Asian companies are beating the pants down of established names in DACs. Companies such as Topping have improved their product so much in terms of specs and usability that established names have to seriously rethink their strategy. The bad part for us is that these Asian companies, once they attain a certain reputation, have started charging what the established companies would charge for their product. But again comes the question - we would happily pay $2000 for a Benchmark DAC. Would we pay $1500 for Topping DAC that has better specs?
Something we all need to think about. Why should I not have two Lepais with one as a standby spare? At 200, it will still be 1/5th of what I have to pay otherwise.