I am not going to comment your thoughts about burn-in.
I do strongly believe in burn-in, or what ever you like to call it.
I got the DT770/80 phones in the beginning of january. They sounded great at first, but when i really started giving the sound some more attention, i discovered that the left bass-end was dramatically "resonating". (Sorry for poor describing) I was really afraid, that the element was broken or something, but decided to try to "burn the phones in".
I let them play music for 100 hours, and then gave them a try.
I tested the different requencies by playing single files with only one frequency at a time. I still got this really powerfull buzzz-noise while playing them, all the way from about 20Hz to 4kHz. But it was still only on the left side. I even made sure, that the problem is the element, not my ears, by flipping the phones wrong way, and by listening to one side of the phones at a time (/with a one ear at a time).
After this, I let the phones play some music for another 100 hours. When I next time put them on, I was amazed: the strangely highlighted bass-line was gone, and both sides felt to be in perfect balance. Since that, the frequencies have been in a balance on both sides. I have now listened over 500 hours of music with these cans, and I just couldn't be more satisfied.
(sorry for the possible typos)