Being based on an external site, it's a sort of quasi-objective quality indicator. Scrolling through the content, it seems to do a very good job of that (though it's still a bit too Touhou heavy for my tastes).
It seems pretty redundant as a quality indicator if evazion's numbers for Touhou are still correct:
The median score for touhou is around 2 or 3 and ~90% of touhou_project_1000_users has a score of 3 or higher. So most touhou_project_1000_users posts have a higher than average score relative to regular touhou posts and will in fact be covered by a touhou score:>x search.