The "thanks" is a holdover from the original karma system. If someone posted, and you felt strongly enough about it, you could click the karma button. Depending on your feelings, you could either like or dislike the post, and karma would be added or subtracted from the poster's karma bank. Some of us had huge karma reserves, and when they liked or disliked a post, it was like getting run over by a truck.
One particularly snarky user had such a huge karma deficit it looked like the national debt. After much consideration, negative karma was discontinued, and positive karma evolved into the thanks button.
Meddle not in the affairs of dragons, for you are crunchy, and taste good with ketchup.