I don't think responsibility has anything to do with it. It's a process, not a job or a chore unless you look at it that way. Staff are still members of the forum, who choose to want to help the community. Some people want to go out on the Internet and pursue and create a humble and friendly place for people to chat online and share ideas. My answer to your post, I believe a community as a whole will add topics and posts.
Well, I think the staff need to be involved with it to a certain degree. The staff can't expect someone else to do it all for them. They have to show they care at least a little bit about the community enough to take part. They can also do exchanges to make it look like the forum is active.
I agree with both @Terminated and @JennyorAlice since we're all members of the same family we all should try to keep the flame alive, but the staff has an extra responsability to make members happy with improvements and other things that encourages other people to join and grow together.
Everyone is responsible. If you join a community and you want to see it succeed, you create threads you're passionate about and hope that someone else will contribute. It's usually easier done when you have threads about movies, video games or the like because a lot of people who are part of this culture usually participate in those. The same could be said for hiking, animals and the like as well though.
The staff can get things started, like Jason said, but they still need to pop in from time to time and still participate. You can't expect your community to do everything. Plus, it may seem off putting to some people if the staff never participates in any of the discussions themselves.
Yeah it's pretty much up to everyone. The Staff need to get the ball rolling with a good few topics before they even think about bringing in new members. Then once people start signing up it's good to engage with the members and be responsive when they have questions.
At the moment, I've slowed down posting on my own site since one of the other Admins has began to post more often (and I'm way ahead of everyone else on post count and want them to catch up), so I'm mostly just answering to peoples questions/suggestions. It's working well enough when you consider we've been a kinda slow site since day 1, but once I get some unrelated stuff out of the way I'll begin engaging with the community more frequently.
The owner & staff create the foundation of the forum. IMO, it's up to the members to keep the community going.
The owner & staff are there to make sure the forum rules are being followed and perform other duties that regular members do not have the ability to perform. They are also there to interact with members by asking questions in the threads/posts they make.
They may or may not create new topics depending on how busy they are with other tasks.
Without the foundation, a house (or in this case a forum) cannot stand alone.