I believe Steem Power is why Steemit can work, users who want to earn more Steem will buy Steem and then hold it as Steem Power. With users wanting to hold Steem Power so they can earn higher rewards there will be less Steem on the market, competition over Steem will increase and demand for Steem will probably be high. It is an amazing system for creating value and generating valuable content as well as rewarding those who actually create the content.