I've talked to one fellow at MetaCritic, and he seemed nice enough, but also really overburdened. I get the feeling that they started out as an independent company and then sold that company or something (not that I really have any idea), but at any rate there certainly seems to be a relatively small staff at MetaCritic proper. I think that the sort of service that they provide is a really valuable one, but it does seem like the list of publications that they consider is... well, aging, frankly. Seems like it was once easier to get in, and now not so much, but again I'm guessing here.
I went ahead and just sent my contact there an email about Out of Eight suggesting that it be considered for inclusion; we'll see what they say, if anything. Personally even if the parent company is the same I don't think there's much of a link between anything MetaCritic does and what GameSpot does (the same is certainly true of IGN-the-reviews-site and Direct2Drive-the-service, which are separate companies-within-the-IGN-parent-company), but again I couldn't say. I really do prefer how MetaCritic handles things compared to RottenTomatoes, though, and that's saying something as I'm a big fan of RottenTomatoes for movies. My only real complaint is that they don't include certain reviewers that I think very much deserve to be included, Out of Eight included.