Based on what I've seen, people haven't been upvoting comments much in comparison to posts.
I'm not sure what the underlying reason is -- perhaps at this point users are more interested in the content and less in the discussion, which is a bit unlike Reddit, where typically the discussion is often more interesting than the post itself.
I think the discussions will increase as the community grows.
Downvoting a post can decrease pending rewards and make it less visible. Common reasons:
Submit
Isn't there something about your voting power going down the more you vote? There, just found a comment about it but I don't have an official source for you. I'm guessing most people want to keep their limited voting power for the actual posts since they feel those rake the most money.
Downvoting a post can decrease pending rewards and make it less visible. Common reasons:
Submit