This is ridiculous. My experience does not match yours, so we get into a big fight over it? I'll answer what I think you asked, then let it go so you can finish:
1. "High" is relative. As I said, my professional experience is IC design, so anything over 50 V is "high" to me. Just like 100 MHz is high to an audio designer, and 1 THz to me.
2. Highest B+ I have seen was ~1200 V in a tube amp with cascode stages. Don't recall the brand as it was a long time ago but it was not ARC. My old ARC amp ran ~600 V B+ (D79). My friend's D90 had around 400 V B+, but a grid at -125 V. An arcing output tube took out a coupling cap and the bias pots. Sometimes bad things happen to good amps.
3. Small (coupling) cap failures I saw in hi-fi amps tended to be due to other failures, like arcing tubes or fading electrolytics/power diodes affecting decoupling caps, as I believe I said. That is when they get exposed to HV, in my experience (which does not match yours, I get it).
4. I have owned a number of tube components through the years but none are in my current system. I recently sold my beloved D79, and have an SP3a1 preamp and a couple of other amps in the closet (one an old Eico EL34 kit rig I just can't seem to walk away from). I sold my tube (ARC) crossover many years ago. I have built numerous Heathkits, tube and SS, but remember few of them. I do miss my old Apache...
5. "Rather, you think most other folks are idiots." I do not see where you got that from my posts, but am tired of apologizing for what I see as a difference in experience.
6. "Do not try to broaden this conversation into areas that we are not concerned with." The topic was capacitor failures; I will concede I brought in experience outside the hi-fi arena, but I have some in that area as well.
7. "Do you think it is rational to routinely change out capacitors from hi fi amps?" No, of course not, and I do not believe I ever said that. I would inspect and measure if I could to determine if a component, any component, needed changing. I have reconditioned older electrolytics when I could and gotten years more use from them.
Hope that covers it - Don