Ok lets be clear that these plots while they are marketing are not bullshit.
The standard equalization for diffuse field ends somewhere around 100Hz on the low end and around 16kHz on the high end. (I can't even hear beyond 15kHz if I am listening to a pure sinusoidal signal that doesn't have any spurious harmonic content).
The vetical scale is a bit large but to be honest isn't too large to figure anything out. Most people have a hard time discerning 1db changes to the equalization of an audio system so it is well within that.
The only thing that annoys me is that they do not give their target curve for the diffuse field equalization (which represents a standard room) and I wish they did. Then I would know how these phones do against free-field response (anechoic chamber). I asume they are not using the IEC standard or they would say it somewhere.
If you're interested both the Neumann KU100 website (in particular: http://www.neumann.com/download.php?download=docu0009.PDF) and the Head Acoustics website (in particular this document, http://www.head-acoustics.de/downloads/eng/application_notes/Equalization_brochure.pdf) have lots of good info. It looks the the SR-LAmbda is about as ideal as it gets for diffuse field response at least according to the Neumann document.