Frequently threads with as few as 3 points make it to the front page. It's (among other things, obviously) about speed of upvotes on /newest- and given that posts rarely get more than a couple upvotes before they're knocked off the front page there, it's a good thing the threshold before things reach the front is low.
Also upvotes by YC peeps, probably have 3 times more weight than normal ones.
Looking at that video, I am inclined to say that this system(HN system) works very well. Almost like magic ;-)
IMO, a high upvote/comment ratio is definitely a sign of a good article.