"Not relevant" is not the same as "not upvoted." There are a number of reasons why a submission does not receive many upvotes which are unrelated to the quality of the content itself, which is why HN has repost rules.
The 10 story minimum is to ensure a reasonable threshold for error and so a single submissions with 1000+ points (e.g. Show HNs) don't skew the results.
Actually if you look at others' analyses[0] some of those sites have a high mean and/or median. On median score alone samaltman.com should be #1. The highest "mainstream" news source would be newyorker.com, it does have a low median, but the average is ~20 times greater.
