Yeah. It's one of things... I anticipate my review being read by some of our friends over at Head-Fi.org, many of them believe in oddball things. Like how a cable sounds for instance.
I've seen opinions on sound quality totally discounted because the reviewer never mentioned a proper "break in" period.
Personally, I believe "break-in" is a placebo. Or, it could be tuning of their own perception. I don't believe most speaker or headphone manufacturers would approve of "break-in".