If coming up with an objective measure of quality was feasible, the voting system could be scrapped entirely, and instead of making a site that allows users to submit links, pg could have written a web crawler.
But web crawler doesn't have an important input: how HN users would vote on a particular submission.
Sorry, I don't get your comment.
I'm just pointing out that it should come as no surprise that the author of this blog post didn't come up with a good metric for judging quality. As in, if the author had come up with such a metric, he would have started a company and become fantastically wealthy applying this magical quality-quantifying algorithm, rather than writing a blog post.
Perhaps. But they are degrees of usefulness, and it's probably possible to do better. Especially if you do an analysis in hindsight, where it's no longer possible for the participants to game the system.