You know, it's difficult for me to conceptualize how Hubski is supposed to work in a simple way. Reddit is very easy to understand; it is, at its heart, a decentralized collection of subreddit-fiefdoms dedicated to different topics. 4chan is just a bunch of open boards where you can freely post threads. Tumblr is a network of blogs following each other. But Hubski at this point is a mishmash of a whole different bunch of functionalities, some of which appear quite redundant. For instance, I don't see what the point of chatter is. It just presents a bunch of disjointed conversations. Sure, it can lead you to where the action is, but then so can sorting by activity, right? The way I understand "Hubski in a nutshell" right now is that it is like one giant RSS feed of threads from which different parts, like particular tags or domains or people, can be filtered at will in various ways for private viewing. I think that's nice because the centralized nature of it brings people together for discussion, while still allowing them to focus on things they find interesting and ignore things they don't.
Okay, try this: You just described three top-down hierarchies. Order is externally imposed. Hubski is a bottom-up hierarchy - order is internally imposed. Whereas Reddit requires categories for content to be posted, Hubski allows content to be categorized after the fact. Whereas Reddit has gatekeepers curating subjects, Hubski has tools for monitoring subjects regardless of who posts it, and posters regardless of their subjects.
I see. That's close to what I suspected was the idea behind it, that Hubski was a single giant, raw RSS feed that can be filtered, split up, and organized in whatever way the individual wants. Like how a single text can be analyzed through many different critical theories or read in many different ways.