Just found this thread. Interesting perspective and I agree on your criticism of the new shoe analogy. Some people have very old headphones which are still strong so one can assume that at reasonable listening levels, headphones don't fatigue to the point of failure. Then what exactly is burn in? I'm not sure.
The only thing that would change my mind is reputable retailers recommending everyone to burn in their headphones or if they even offered such a service. I've found some mentioning burn in and adjustment as a reason to not immediately return a headphone, however they never exactly explain what burn in is or how you should go about it. I mean, if I owned a store that sold headphones, I'd plug a phone into a system, leave it on for 200 hours and sell it for $50 more and I'm reasonably sure people would buy it because time is money. But no one does, probably due to warranty disputes.
So here I am, not sure of burn in. My headphones sound as good as they ever did. Going from the k701 which is light on the bass to the 840 makes me feel nauseous at first but then I understand the sound after a minute or so. Kind of like driving someone else's car - you need some times to get use to the gearbox and clutch, as well as the handling. Could burn in be that as well as some physical changes to the drivers? Not sure.
Burn in has affected my life twofold. Firstly, it made me play my PX200 for hours when I got them way back in 2005. Each time I picked them up I was amazed with the apparent improvement. This time around, I did no burn in and to be completely honest, I can't hear a difference as I play more music. I estimate I've racked up 20-30 hours on both headphones so it's arguable that I've not finished burn in and this is fairly easy to suggest with the k701. Could it be that the reason why I my experiences differ is due to my initial belief or disbelief in burn in? That would infer that it was purely psychological. I can't really say. Secondly, it's given me a chance to discuss the issue at various places, online and in real life. All of my friends believe in burn in and a fair few are much smarter than me in all areas. I often cast doubts over my perspective due to them believing the contrary but then again, that's justification of why burn in should be believed at this site. Just because some senior members believe in it doesn't mean I should take it as gospel.
YMMV should always be said and it's ok if it does vary from others. Whether burn in is physical or psychological is irrelevant. If you think/believe that headphones sound better over time, listen to music and enjoy the change. If you don't, listen to the music and enjoy the constantly great sound. You can't really lose can you?