Several people may read an article and come up with the same reasoning. If you wait until you read ALL posts of a thread before posting, you may find that you will never get to the end (someone is ALWAYS posting it seems).
And sometimes I do read it to the end (when it's still short) and no one has made the comment I want to make. I post (sometimes editing it a lot) and I find that when I post it, in the interval between when I started composing a reply and when I hit the "post" button, someone else has already gotten in and said it already.