Guy:
Why? What makes an author's older work less relevant and less worthy of comment than his/her newer stories?
I would not say that age makes an authors work less relevant or less worthy, I just thought the comments on older stories are not so relevant. But if you authors still appreciate comments, it's okay. I will try to comment more on older stories as well in future.
But I still want to point out that the amount of comments is not an appropriate measure for the quality or worth of a story, especially not for stories with few comments. Another reason may be that "funny" stories in general get more comments, because it is so much easier to respond to some funny themes, where a reader must not explain his/her emotions or involvement. I myself comment less on stories which really touch me, because it's quite hard for me to express my own feelings and emotions. So if I don't comment, the reason can either be that I like the story too much or that I'm not interested at all. Most likely I comment on stories which I like, but where I am not too much emotionally involved.
Therefore my advise to all authors would be, not to overrate the importance of the absolut amount of comments given to one author or one story, especially not in terms of worthiness of specific stories.