Further, Microsoft and Netscape are both using IRC as their kernel conference tool of choice. The only way to guarantee access to a server is to control it. Channel topics can be public or private. Therefore there is no way to subscribe or unsubscribe to topics. If they exist, they simply exist.
Channels are dynamic.
When the last user leaves, the channel disappears. Access by users or clients to the IRC server can be controlled, however. This control is fairly well developed and can be tuned very finely.