Yes, some of them are far from flat, that's because of the diffuse-field equalization used on the best models.
The proximity effect directly opposes the diffuse-field equalization that is showing in these graphs and form a flat frequency response.
Also, I highly doubt you can get this flat of a frequency response with speakers, unless you pay $200k for room treatment and HUGE far field monitors with triamping. There is NO WAY small chineese asian cheapo nearfields will get even CLOSE to this flat.
Headphones are made to compensate for the ears and isolate the room.
Speakers, when put into a less than perfect room, tend to sound bad and speaker manufacturers don't take into account the morphology of the headphone user...so there you go...all in all, headphones are much flatter than monitors $ for $
Obviously, a great tuned room with far fields would be my preference over headphones, but who has this luxury ?