Thanks RabbM, but what I meant was that there's no way to copy the episode description text from within the iTunes player. Anyway, after the expected "We've reposted the videos to your account" response, and (again, as expected) no descriptions attached, I emailed them again with a screenshot of a recent file and an older one both opened in Subler, and showing quite clearly that no Description or Long Description tags were set (plus a link to this discussion page). Hopefully it will be fixed within iTunes 11.
Exactly when a content provider's tags in their XML file get written to the actual video file is a mystery to me (but, considering if you do a "Get info" on a file while it is still downloading in iTunes it does not show any info for most of the tags, I guess it is done on the user's Mac and Apple sends the XML data as a separate part of the download), but my guess is an Apple "Genius" disabled the description tags either from being requested by the iTunes player, or sent by the Apple server.