Then I realised that maybe that's not the way to look at it. The person who blogged or wrote the article may not be the one returning the favour and reading your blog/article and commenting back. It may be someone that read your comment and decided to read your blog/article. They would comment on yours, you would read theirs, comment and so the whole thing just snowballs.
So what am I suggesting? You don't have to write this Nobel Prize winning comment. Just a simply "Good article/Interesting viewpoint/Never thought of it that way" comment would probably go a long way to encourage the author. At least it shows that you read what they had to say and stirred an opinion in you. After all, isn't that what blogging/article writing is all about? Voicing our opinions and stirring opinions in others?
At least that's my opinion.
So it's up to you now to comment and tell me if you share my opinion, or have one on your own on the subject. Who knows? It could be the start of a long and prosperous relationship of mutual commenting :-)