Some comments are on-topic and are helpful, some are on-topic and humorous. Some are off-topic and also helpful, some are off-topic and worthless. As so on, and so on.
With only one direction we can "push" a comment (and only one direction with which we can view comments, up & down), there is not all that much filtering that can go on.
Sometimes I enjoy reading the "funny" responses. What if this was a separate comment axis that I could view? Others may not be interested in such a thing, and could ignore it.
In any case, the format of HN doesn't lend itself well when people from all over the world bring their own views into a single topic. I don't know if a good way of solving it easily other than being ruthless about removing content that doesn't belong.