I think, you are confusing referrals with MLM...referrals doesn't cost anything from user and only person who joins through referrals would share very small percentage of future earnings, which they don't even have to see. Also people who referred them have incentive to support them by voting, because it will, not only gives them pleasure to do so (because they are friends, family) but they also receive small extra reward. Just like curation, you like the content you vote and you also get small reward.
RE: eSteem and Steem referrals, incentivize users to invite friends