Comment by bitshiftfaced

When you consider the submission itself, the upvotes it receives usually is praise. If you can see it listed not far from the home page, people probably upvoted it more than downvoted.

Also, there's probably bias in that the less work and mental effort required of a comment, the more likely you will make it. Fault-finding can be productive, while "good job" comments maybe not so much. Therefore, the combination of that sort of comment being "easy" to make while also being perceived as more useful and more likely upvoted explains why we see more of them, to me anyway.