I would not take too seriously Bryston saying their amps should be plugged directly into the wall. This sentence was probably written by their lawyer. It is a polite way of saying; if we blow up the amp playing around with the power, then it is not their responsibility.
All Blue Circle tube gear has wording in the manual saying there are NO user serviceable parts; so the case should not be opened under any circumstances. Now almost every audiophile who buys tube gear will most likely experiment with different tubes at some point. I am sure Blue Circle knows this. But once again they are politely saying that we roll tubes at our own risk. Even without tube rolling, how many people ship gear back the the manufacturer even to have worn tubes replaced?
I've also seen manuals for gear that has an IEC socket have wording to the effect that we should only use the supplied power cord. Now, why put on an IEC, if we have to use their power cord? Once again is it their lawyer talking CYA.