Why no “Break in” period?

Time heals all wounds.

Not true.

accommodation

Never heard the word used in this way. Is this a medical term?

Electronics do not have a break in period

Either everyone is undergoing neural "accommodation" or your statement is incorrect.

Line conditioners have a break in period after that they sound more dynamic and open.

Electronics do not have a break in period. You are only accommodating to the sound of your system. Your first impression is the right one.


As for Paul McGowen, he will tell you what ever it takes to sell his equipment. He is not Ralph Karsten, Nelson Pass or John Curl. You have to take whatever he says with a grain of salt.

Nelson Pass, John Curl, and Ralph Karsten all believe in equipment break-in, burn-in, or what ever you want to call it. The late Charles Hansen did as well.

Nelson Pass, John Curl, and Ralph Karsten all believe in equipment break-in, burn-in, or what ever you want to call it. The late Charles Hansen did as well.

The point wouldn't be that some electronics designers think AUDIBLE break in occurs (note the capitalized word),  but what evidence they have for the claim.

Do they have objective measurements showing the change


and

Do they have tests correlating the objective changes with their audible consequences, that control for well known listener biases?


If not, it's just more of the same audiophile anecdotes, unfortunately.

jea don't kid yourself. The manufacturers have to remain politically correct or people won't by their equipment. You have to be a personal friend to know what they really think. 
Noromance, I did not make up that expression but in most relatively minor cases it is quite true. Obviously not if your child gets killed in a car wreck. 
Accommodation is used as a medical term and you are right. Everyone is accommodating all the time to numerous stimuli. 
All those guys "burn in" their equipment primarily to make sure they are working up to snuff and nothing is going to blow on the customer. 
Having said all that, just think about it from a manufacturer's standpoint. The customer calls because things don't sound just right. The easiest come back is, "well you have to break it in." Withing a few days or weeks the customer gets use to the sound and things are peachy keen. He thinks the unit broke in when in reality it is he that broke in. The human brain is way more flexible (and unpredictable) than an amplifier. Many companies now put something in their manuals like, "don't worry if it sound like crap. It takes three months for it to break in." When people don't know why they make stuff up. The Greeks made up Zeus. A very creative explanation for lightening.
Anyone care to give us just one proven reason why a purely electronic unit's sound should improve after manufacturer's burn in?
My ESLs break in because the diaphragms are initially over tensioned by a heat gun at the factory and it takes about 100 hours of play time for them to loosen up to the proper tension. The factory does not do it for obvious reasons.