>> I'd say it is more than a temporary glitch if they post that elaborate a notice.
Not necessarily. Any large site like that, that services a big customer base, must have a boilerplate message ready to post when they have to take the site down. And they would have to, from time to time, however briefly, to install any new element (graphic, link, procedure, whatever).
I've encountered periodic "unavailable" messages at most of the ordering sites I visit with any frequency.