Why a 10 point scale?

We get to rate articles on a scale of up to ten stars. Why?

Practically speaking, it seems that if you really like an article and want to put it on the recommended list, you rate it 10. All the top articles are all-10's. But that means if you rate something 8 stars or 9, which sounds like a really good rating, you're actually hurting its chances, by putting its average score below the others, as far as I can tell. Unless Gather uses a cumulative point system, but if so, that's really not documented or intuitive, so we need a better explanation.

What use is there for rating something at 4 stars, or 5, or 6? Practically speaking, does anyone ever do it? Is there any chance whatsoever of coming to a community consensus about what middle ratings like that actually mean, so different people will use them in the same way? (I don't think so, but maybe there's something I haven't thought of).

Daily Kos used to have a 4-point scale for rating comments, but that turned out to be too much. If a 3 is good and a 4 is excellent, why would you rate something 3 and bring its average down? 1's were used consistently for "bad" ratings, but 2's weren't clear. MyDD, Daily Kos' "blog parent", uses a 3-point scale for rating comments. Daily Kos itself moved to a new system where you can simply give a +1 (or, if you have high karma, a -1) to a comment. And all Scoop & Soapblox blogs use a simple "either recommend the article, or don't" system for top level posts.

How is the rating system on Gather supposed to work? What's the goal?