Its a reasonable analogy, but were not there yet. While mastodon instances will talk to mastodon instances, and pixelfed instances will talk to pixelfed instances, and kbin instances will talk to kbin instances, at the moment the intercommunication between apps is a real issue. Imagine postfix wouldn't reliably talk to exchange servers, that would be a real barrier to adoption. I'm hopeful this will get sorted, but were on the bleeding edge at the moment.