Well I would say if the question is directly asked of your comment then you should reply. If it's more a general question in relation to the article then the blog owner. I think it's expected if someone questions your particular comment for you to answer.
Example if I comment on a NFL blog and say the Cowboys are going to the superbowl! And someone ask what planet I'm on. Well the blog owner may be thinking the same thing. So I would have to answer that myself and say the planet of Texas!! Hope this helps. Go Cowboys,,