I agree with you and luisdent completely - I am not talking about compensating for obvious differences in sound. For example, I have never liked the HD650 and no amount of listening will make me grow accustomed to its signature.
What I am talking about is what many people refer to as "burn-in." It is simply acclimatization.
My first pair of "serious" headphones was the HD 650. I always thought they lacked "life" but I had nothing to compare them to. The first time I heard the HD 800 I thought they were intolerably bright and thin sounding. Eventually, I replaced the HD 650 with the HD 600. I much preferred the HD 600 and enjoyed them for quite some time. It was during this period that I had another opportunity to listen to the HD 800. Well, I think you know where this is going...they were astounding! What happened to that shrill, bright, tinny sounding headphone? Obviously, nothing changed except for my perception.
Oh, yes. People absolutely "burn-in" their brain with a new headphone they haven't heard. I think this shows by how many people think the sound "burns in" so much after so many hours of use, when studies and graphs have shown, that while there is, or might be, a small change in sound it is almost always practically inaudible levels. I think it is usually more the brain getting used to something for sure.