One cool feature of Scuttlebot is that if you and your friend are already following each other, you only need a connection to each other P2P to be able to send messages to each other. So if you're on a train with ad-hoc WiFi connected to each other, you can still proceed as usual and sync stuff.
I don't think this feature exists in Usenet and BBS's where there is a central server who masterminds the sync that everyone is doing. Same with email, requires a server (local or remote) to send/receive stuff while in SSB both local and remote are usually the same machine.
For BBSs, you're correct. Usenet (and email) used UUCP, which is actually much closer in concept I think here.
UUCP is a store-and-forward mechanism, not dependent on a real-time connection to a particular server. I used to run a node, connected to a guy I'd met who worked for an ISP. He had, gasp, a full-time network connection via ISDN; pretty magical in these days of dial up.
So, Usenet feeds were configured on my own little system, essentially subscribing to the newsgroups I wanted. Periodically, it would dial out to the other gent, upload any new posts from me, and download anything new on those newsgroups. My email came and went the same way. Naturally, what I got was a subset of what he had accessible.
While I never used this functionality, I could have had others call up to me, and I would just be an intermediate link in the chain. RFC 976 (https://tools.ietf.org/html/rfc976) describes how this works for email, including SMTP over UUCP.
I don't think this feature exists in Usenet and BBS's where there is a central server who masterminds the sync that everyone is doing. Same with email, requires a server (local or remote) to send/receive stuff while in SSB both local and remote are usually the same machine.