Money comes from production that is valuable to others. It's also a store of your and other's production in a game just as much as it is in real life.
Steemit is "mined" each day, and it is given out based on upvotes. The more Steem Power a person has, the more of the daily production is controlled by them. That is how I've understood things at least.
I guess the production on Steemit could be considered the content added to the blockchain? Then the better content is rewarded more as better production in real life would be rewarded more.
That's right. Popularity is assumed to imply quality; which I'm sure is horrific to those who subscribe to the Labor Theory of Value.