What I don't quite understand is why people seem to think star-ratings are only of value to the person whose work is being rated. When I go to YouTube, I immediately sort by ratings. The ratings are anonymous. The point is that now I can see how everyone else liked the item, which is usually a good predictor of how much I'll like it. It only takes a few people (no more than 5) for a good average score to come up.
Even with sites like Yelp.com (if you haven't already checked that site out, do), where people do leave comments, I rarely read them... I really just sort by rating, since that really helps (and I've found a lot of good restaurants that way).
I want the rating system to primarily serve that purpose. You watch it/view it/use it, and now, since you are a nice person, you want to let other people know to watch it/view it/use it too.
Not to mention, I'm a bit afraid that people will just not rate as much if they are forced to leave a named message. First, it's more of a hassle, so naturally people won't want to do it. Second, concerns about PMing/rate-backlashes are real, and will tend to decrease honesty on the site.
-Jake