But the main question still is: who legitimately ownes the sound. Can an amp manufacturer really claim ownership on a 5E3 or a modified 5E3 circuit? I mean, loads of amps are based on that particular circuit.
Yeah, the whole realm of intellectual property is a complex and ever changing landscape. And society at present is actually hostile to the ownership of IP, i.e. "copyrights / patents are evil and should be abolished!" This, of course, from people looking for some way of getting all of our hard work for free without feeling like a thief.
Who owns the sound is trickier still. If Kemper is doing Bad Things by miking an amp, does that also apply to the recording studio and record company who released the Zep albums? Hard to come up with a completely black and white answer to this sort of thing.
In my case, while I sold all my amps when I bought the Kemper, part of it was because they were decades old and twitchy. If When I buy amps in the future, those purchases will likely be driven by the fact that I got to experience Friedmans, Bogners, etc. in the Kemper and fell in love with them. So, yet another bit of grey.
I'm not certain that amp sales dramatically decreased over the last years.
I don't know what the numbers are either. I do know that guitar sales in general have diminished in part because the younger generation (always the prime market for music related things) relates more to Rap, EDM and other forms of music that are less guitar-centric. That would certainly put a dent in amp sales.
On the other hand, I'm seeing a trend in tube amps where it's common to include built in attenuators. I had a Vox AC 15 that ran at something like 15 watts, half that, and then something like a quarter watt. And sounded good at all levels. Same with an EVH lunchbox I had. My 20 year old 50w Marshall, on the other hand, simply had to be cranked to tinnitus-inspiring levels to get "that sound."
I think this is due in part to the fact that while there are still people who like playing guitar (and metal is currently popular), there are fewer gigs for electric guitar music. And the ones that are out there are much smaller rooms. There are also bedroom players who have a family, career and a full schedule. They have no interest in gigging but still enjoy playing because, well, it's good for the soul. Neighbors banging on your wall, however, aren't.
So, I think part of the tube amp stuff is just evolution in action. Now if I could just figure out how to grow a tail. Because that would be so cool on stage...