I imagine receiving dislikes wouldn't be rewarding, however the up/down buttons do not convey that kind of information. All they can fundamentally tell you is that someone (assuming appropriate bot protection is in place) pressed a button in proximity to your comment. There is no other information attached with the action. It could be purely accidental for all you know. Knowing that people have loaded your comment in order for the button to be presented, and thus statistically are likely to have read it, should be rewarding, though. After all, wanting others to read your work is why you're writing in a public forum and not your private journal.