Hello.
I can answer for the C library. Libstrophe is low-level library and provides interface for creating, sending and receiving xmpp stanzas. It performs connection and authentication process, but you need to implement any high-level logic by your own. This is the idea to build everything from bricks. Libstrophe allows you to implement pubsub, but this will be not 1-2 calls of the interface functions.
I think the best example will be project
Profanity. It doesn't implement pubsub, but shows how to use the library.
So short answer is that libstrophe doesn't provides pubsub interface, but allows to implement it.
P.S. There is google group for the JavaScript Strophe:
https://groups.google.com/forum/#!forum/strophe. You can repeat your question there as well.