I've read that graph (along with pretty much everything there is on innerfidelity, Headroom and Golden Ears) dozens and dozens of times (if not more).
Did you read my comments about Tyll's interpretation of the HD800's graphs and them being amongst the very best that he's measured? We spent quite a bit of time on the phone doing this work and the one thing I do strongly remember was Tyll's very high regard for the technical abilities of the HD800s.
FYI...some further suggested reading on headphone measurements:
(have a look at the author of the second article...so yes, I am a little familiar with audio measurements of the hd800s though no where as close as Tyll).
And please note that those are raw measurements and not adjusted to represent what we actually hear like on the graphs on innerfideltiy.com or Headrom.
Edited by MacedonianHero - 12/9/12 at 9:28pm