even if 'Options/Syndication Feeds/For each article, show:Full Text' is ON, everything that goes after _MORE_TEXT_TAG_ is not showed up in the RSS reader.
I beleive such feed export behavior is wrong.
at the very least, it'd be _very_ nice to have some kind of a "Read on..." pointer (at the entry bottom) in this case for the feed readers.
but this does not 'solve' a WP.com "backup" problem: it'll require to edit all that paged posts to have a full text to be exported.
meanwhile, beware when you page your post.