One thing that often happens is that hackers, hunting and reading late at night (like me) submit something to YC News. But basically nobody's reading the news feed, and four or five hours later, one or two votes isn't enough to get something on the front page, which is sometimes needed to get recognized by many people.
I have a good metric for this: sometimes I'll submit something and it won't hit the front page at all. But one by one, over the next few weeks, votes trickle in. This must be from: (a) people reading my submission history, or (b) people submitting the same article. But because I submitted at a time when nobody was reading it, it never even gets a chance to hit the front page.
Edit: I did not notice gaika's similar, elegant proposal above. But if two people make the same sort of comments independently, it should say something.
You then sort this new feed like the front page (though perhaps with nonzero start points) -- so there's both decay and a chance that good articles without a ton of initial votes, eventually get up there (though perhaps on slow news days).