I understand that upvoting someone's comment will not give them any reputation points, and I'm fine with that. I have no desire to change this functionality.
However, I AM curious - what was the original reason for setting it up that way and not, say, give someone 1 rep point each time their comment gets upvoted?
There have been occasional questions about this on the meta.stachexchange, or back when it was meta.stackoverflow, including this answer that explains why they aren't going to change the behavior.
The answer there doesn't come right out and say it, but the reason that comments don't have rep is because rep is for good questions and good answers. There's really no such this as a "good comment" or "bad comment", apart from obvious policy violations (spam, harrassment, etc).
The idea of comments is that they are transitory. After a while, you don't even see them; in fact, it's not uncommon for users to go back and delete old comments, or for moderators to come in and delete comments en masse when thy get particularly out of hand. That kind of variability would play havoc with a rep system.
Getting reputation for comments would essentially elevate them to the same level as questions and answers, when they are purposefully intended to be second-class citizens. We don't want people getting a "reputation" for being a really good commenter, because ultimately that doesn't advance the goal of Stack Exchange: to explicitly not be a comments forum.
Lastly, if you allowed + rep points for comment upvotes, you'd ultimately need to allow - rep points for comment downvotes, but it's not clear what a downvote on a comment would mean. Comments often contain opinions, suggestions, or requests for clarification -- we don't want people penalized for making suggestions that just happen to turn out to be bad.
