The primary difference between Steemit and all revenue sharing systems is that Steem doesn't share revenue, it simply tracks relative contribution. Any and all economic value attributed to Steem is perceived value of the platform and its potential to be used as a cryptocurrency. 

Steem is mathematically always able to reward contributors with *something* so long as there are people who want to work together to improve the platform. If the market cap falls, it just means the rewards are smaller in dollar terms, but just as large in percentage terms. 

The users are directly responsible for building a community people want to participate in. It is the growth of the community that brings value. 

Stated another way, you can get away with slave labor wages if the slaves are earning equity in the startup. They know their payout is not the cash they earn today, but the future value it will have when the platform grows.

Revenue sharing systems struggle because the revenue is so small relative to the value added by the network effect.