(aside: 51 points but only 1 comment? It's a front-page worthy article, but sort of feels like there's some vote gaming happening. I've never seen 50 points w/ 1 comment.)
My theory is that it's a sign of a good article, because more energy is going into reading it than into posting quick comments (which are usually less valuable comments). But I don't have the data.
Edit: well... we have the data (to test this), but it would be enough of a pain to do the analysis that other things will probably take precedence forever.
But hey I just commented :)
On this post, I started reading, then paused to hurry back and upvote on HN, to do my part to keep it from falling off the front page, before I returned to finish reading.
Measure the time between when someone clicks a link to the article and when they upvote it, compare that to one of the "estimated reading time" metrics of the linked page...
(Which, of course won't work, because at least some people (ie me) open a bunch of tabs for everything that looks interesting on the homepage, then spend a few minutes at a time over the entire morning choosing a tab and reading/voting...)