In a way you could say we have the opportunity for multiple revenue streams. There's the traditional pay for work done in the form of the post. This is kind of like when I write a magazine article; I only get paid once and wouldn't expect to be paid indefinitely. Then the passive income can come from curation rewards, especially if you use an autovoter. You just have to collect them now and again. This could also be compared to earning interest on savings and the more you save the more interest you get. You could also view this as being paid to read, because if you like what you read your vote gives them some money and you earn some in return.

Then, as you say, if an old post stays relevant and starts conversation you can potentially earn over again. Being paid for conversation.

I also liked how @holoz0r put it as a comparison to patreon. We get to reward content creators for free. So many options!