This seems like it could help. I tend to read a submission, and maybe a few of the early comments, and then it just stews in my brain for a bit. Maybe an hour or two later I will suddenly have a fully formed idea to share, but by then the story has already left the front page, so I just don't bother commenting. It's not that I only want to comment if I think I am going to get points, but I only want to comment if I think someone is going to read it. I don't really see a point in just shouting out into the void.
Also, having the stories leave the front page so quickly encourages people who are just interested in getting points to throw out whatever garbage they can in hopes of grabbing a few upvotes by being one of only a few comments on a given submission.