I'm reading this thread closely and would like to add for the sake of precise arguments and hence conclusions.
There's a difference between burn-in and deterioration and I see you mix these terms occasionally.
This is deterioration, and what you talk about when you say magnets loose their properties, or materials become softer or entropy etc. This is not a case for "burn-in" crowd since no one here or in his right mind would ever make such a silly claim to say speaker never deteriorate and always sounds the same:
This is how burn-in would look like (although it should hold the peak for at least some time to be more accurate). Your unit under performs when new, you bring it to its level and after awhile it starts dropping.
To me personally, even making such a dubious claim that a company knows and calculates in where the performance will be after a 100 or 350 hours is just unacceptable.
You burn in your ear. Marketing uses this to make you go through the adapting period and stick with your choice (not claim for refund) by saying listen to it for some time while it burns in (for me dead give away is the fact that they always tell you not to let it play on its own while you're at work - of course, no owner's ear, no break-in).
It's very hard to notice the slow process of deterioration and most of us will notice it only when AB compared very old speaker to a new one. At this point we might even opt for the old one simply for habit and this is why brochure tells us to break-in the new gear. It happens all the time, after spending 200 or more hours with a new unit, there's no going back or hardly ever.
