I won't pretend my marksmanship skills are good enough to definitively say there is a difference. But when I have broken in new barrels by the book, slowly increasing the number of shots in between cleanings, up to 100, I have had great performance. Would it have been just as good if I had been a little less stringent? Dunno. But I would rather be redundant and get it right the first time. If I am going to complain to a manufacturer about accuracy, I should be able to tell them I did everything I was supposed to. Maybe one day I can get two identical rifles and do a Mythbusters style comparison to see if there is a difference. That's two Saturdays, two rifles, and a couple hundred rounds extra that I don't have right now.
Also, it's a matter of discipline. taking the novelty and jitters out of having a new gun, and forcing myself to be serious about using, learning, and maintaining it. Like I learned in the army (and I will have my kids learn as well,) that having a gun is about carrying, maintaining, and securing it as well as firing it. Kind of a ritual to remember the important stuff.