If what they call 'consistency' is just the total number of stories posted, it's not really surprising to see a strong correlation with total karma points, is it? The more stories posted, the more karma gathered. Anything else would be a real head scratcher.

You could say, there might be people who keep posting stories even though the don't get upvoted, but that would be kind of irrational. If the community doesn't seem to be interested in what they post, they will stop doing so sooner or later.