actually it's not zero. its 0.8 or 0.9 or something like that decimals depend on your steem power. i find out that when i up-vote someone and i gave them +1 cent and then up-voted someone and it did nothing. that means that someone like me that had 0.8-0.9 value up-voted before me and did nothing then i up-voted and changed value. so new users don't worry. after upvoting even if price does not go up does not mean you did nothing and you will still get curation reward based on price of course.