Sure I can understand the pathways in the brain adapting to a different type of sound, once you use headphones for some time and condition your brain to the sound of headphones but I have never experienced it. Yes I have read about it quite a bit and have puzzled over it. Well I guess you guys get to experience something I don't. Shucks. :^)
Ultrasones (and thus most likely most headphones) sure benefit from burn-in. As I normally listen to my burned-in ones and recently I listened to a not burned-in pair (I didn't know before auditioning that they were not burned-in) I can state without a doubt it makes a world of a difference and for sure not in my head.