This is true, but the comparison also raises a further question: do Twitter, HN, other places support kinds of discussion besides this, and to what extent? And

This is true, but the comparison also raises a further question: do Twitter, HN, other places support kinds of discussion besides this, and to what extent? And depending on the answer, are they worth participating in? I think that part of the OP's point is that Twitter is strongly inclined to this kind of interaction, which has to factor into a person's decision whether to use it.