The basic difference is that the person publishing the post curates where it will go and how it will be defined/labeled/tagged. They then send it off to the appropriate relay. Then, everyone reading from that relay (because they are interested in the same topic or are part of the same community) can see it and respond to it.
The people who want to read it have it _sent to them_ over the relay. Or they go to a client where there's nothing but Stuff Like That.
They don't have to go dig it out of the gigantic heap of Bitcoin memes and EXTRA LARGE TEXT RESPONDING TO EXTRA LARGE TEXT.