the fact that they have HN as having 2.4 times more referrer traffic than reddit makes me question this. Look at the numbers, HN is a top 3,000 site, reddit is a top 300 site.
Indeed. Speaking as someone who has had several articles at the top of HN and reddit-programming, as well as several on proper reddit as well as digg: it's total nonsense. I'll get 5-10k hits, for a "decent" HN story, I'll get 20k+ for proggit. For a #1 HN story, I'll get maybe 20k hits, and 40k+ for a #1 proggit.
Top-level front-page reddit is pushing 100k.
Here's an example of the traffic of a recent article that got both HN and proggit: http://imgur.com/TpQ5T Obviously, n=1 here, but this pattern repeats all the time.