Our markup is based purely on cost of parts and labour, also we proactively look to improve the reliability of our gear. We just see the 20 year warranty as our way of saying we believe in our product.
Our amps have a thermal shutdown safety on each channel, assuming the circuit is working the worst case would be the channel shutdown prematurely. As fo shorts, each Bryston amp has a combination of fuses and circuit breakers, so shorts that may occur shouldn't do any permanent damage. I could be mistaken, but most of our warranty work an amplifiers if usually with the switches on the back. This was one of the improvements that came to the 2.5B, the switches are no longer in the audio path, rather they trigger sealed relays. The relay switch combo is just one example of how we actively look for ways to further bullet proof our gear. Before any one asks why don't any of the other amps have this, it's just the 2.5B is the most recent to be released and how many people have posted "my 4b is in to get a switch replaced". Until that happens the 4b has and all our other amps have 20 year warranty.
Cheers
Chris