Audio Research guarrantees their tubes for a time period so if they take out an amp, they should repair it, and obviously do.
Regarding a tube taking out the resistors and some circuit traces, Audio Research feels, I think, that there are compromises inherent in designs which protect the amp in the event of tube failure. It would obviously be easier on them the design amps that way, fewer repairs, but they are a perfectionist company and strive to have no shortcuts to sound quality. I am not saying that other companies are taking shortcuts, just a different approach.
Regarding a tube taking out the resistors and some circuit traces, Audio Research feels, I think, that there are compromises inherent in designs which protect the amp in the event of tube failure. It would obviously be easier on them the design amps that way, fewer repairs, but they are a perfectionist company and strive to have no shortcuts to sound quality. I am not saying that other companies are taking shortcuts, just a different approach.