Comments are a difficult thing at times. Some days there is just to much content to vote on and comments, at least for me do take some time and thought, so even though I want to leave comments, sometimes I am at a loss for words, or just plain assed talked out.
I have seen some of those "just for the sake of it" type comments @bozz mentioned myself, but there are or seem to be more meaningful comments being left lately, at least I the post that I read/view.