Many speaker manufacturers (including my fav Paradigm) do talk about speaker burn-in, but the info at
http://www.gr-research.com/myths.htm is the kind of info that makes the sciency/nerdy part of me cringe. They seem to be throwing around a lot of terms that sound as if they are important, but they do not offer definitions of the terms nor do they cover the methodology of the measurements they say they made - which makes me think that they are trying to C their A in case some of their customers (this is a commercial site selling speaker kits) don't like what they have bought. In other words, this seems to be a page written by a marketer with specious information. Speakers can and often do sound different than they do in a showroom. Perhaps saying that speakers take time to burn in are efforts to alleviate the concerns of the fact that speakers will almost certainly sound somewhat different in a user's audio room than they do in a show room.
Even Pardigm has been called out on their marketing that says the curved cabinet designs for their higher end speakers breaks up internal standing waves and, supposedly, makes the speakers sound better. In particular,
this review of the Prestige 95F speaker states it outright.
There is a thread at
Audioholics that specifically covers the gr-research page. In particular,
this post from the thread indicates that Gene from Audioholics has busted the myth of speaker burn in.
A bit more searching reveals
the article Gene from Audioholics authored, and which states, in a more scientific manner, that burn in effects are minimal for speakers at least. I tend to believe Audioholics - it was in a forum thread at Audioholics where the lack of audible difference between coat hangers and pricey speaker wire was demonstrated.