As a commenter, I often have some difficulty to comment on the very interesting or thought provoking pages.
Sometimes, they make me think of so many different things, or initiate a so intricate thought process, that it would take a lot of time to organize my thoughts and write them down in a way that is understandable for the creator. Plus, it may encourage a discussion, and I may want to avoid it, not because I don't want to discuss, but because I know it will again take me long to organize my thoughts etc, and I feel it's a responsability I take, when I start a discussion, and that abandoning it would not be ok.
So, I limit my long comments, and generally keep them for a handful of stories only.