I don't think the metafandom thing is intentional (though I do have a vague memory that they used to link to both versions of crossposts - or is that linkspam that does that? Not sure.) Anyway, I suspect it's that most of the metafandom mods are DW people at this point, so they link to the posts they see on their flists. And that they post via the DW crossposter, so unspecified user-name links automatically link to the DW user, which makes it easier all 'round.

I am definitely looking forward to one of the DW developers figuring out how to put links back to other crossposted entries on the DW entry, though, so I can easily get to the discussion on both sites.