Why no “Break in” period?

If you suffer from expectation bias and tend to fool yourself, you should not be in this hobby, and I have some $5k cables you might be interested in buying.

"expectation bias"

One of the best statements to be said with new gear, and Ralph (Atmasphere) as far as I know was the first to use it here on Audiogon forums.

Yes, what a lovely phrase! It carries the same force as the phrase, "skepticism bias". :)

And now I return to my writing, as it is a waste of life to argue such things beyond a sentence or two. I have been known to be drawn into such things in the past, but I'm trying to reform myself.  :) 

That's OK Doug. You hang back and I'll light the fire.
Certain mechanical devices like cartridges and speakers do indeed have  break in periods. 
All of our central nervous systems exhibit a characteristic called accommodation. All of you have done it numerous times under a plethora of circumstances. Your ears accommodate to loud volumes. Your sense of smell accommodates to noxious odors. Your vision accommodates to lighting. You even accommodate emotionally. Time heals all wounds.
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. As for PS audio, their designs have gotten better over the years and you can not argue with the business model.   

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.