People tend to put too much emphasis on the upper treble when it comes to determining whether a headphone is bright or not. Yes, the HE-400 is bright in the upper treble as there's a big peak there. However, the HE-400 is overall a dark headphone. If I were to EQ the upper treble of the HE-400 down and compare it to say, an LCD2, I'd say the LCD2 is the brighter headphone because it has much more upper mids-- about 6db more from 3khz to 5khz.
HE400s are emphasized in mid-treble too (8k-11kHz or so) and I think that's where most of the perception of brightness comes from. Upper treble is overrated in terms of their impact on overall performance IMO.