Votes on Steemit are not equally weighted. It is possible for somebody with a lot of Steem Power to leave a comment on a post and upvote their own comment solely for the purpose of extracting a large percentage of the curation rewards. My post here pertain to upvoting your own comments as that is more controversial on Steemit then upvoting your own post. Although, upvoting your own post is also something that you can do to exploit the way the reward pool works. Check out the hashtag #rewardpoolrape or #rewardpoolrapist and you'll see some abuse out there.