I think you make an excellent point that due to the fact that we all hear a bit differently (age, biology, what we think good sound sounds like) some will like the HD800 better than its younger bro. Actually it makes it harder when I was going back and forth between the two to give a decent eval, because I am more used to the HD800 sound and the slight loss of air around instruments in the youngster is, at first, a point in favor of the HD800 (even if that air is due to the extra treble energy). But there is no evidence to suggest that the new headphones were designed by younger engineers. I think the far more likely theory is that the genre of music that audiophiles listen to has changed a lot, which is due to a shift in the age demographic as well as the fact that headphones have a much broader appeal now, then when the HD800 was released. And finally there has been so much written about the 6khz resonance peak. Tyll even did his big sound series using a modded HD800. So it makes sense that Senn would release their own mod. But yes the HD800 is still either the best or second best dynamic headphone on the market, so no need for anyone to freak.
Also, although my ears are old, I could easily hear that old Yes albums sounded less grainy and not as distorted when the tracks became over modulated on the HD800 S.