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.
In a well populated and functional forum, staff shouldn't need to create new topics. Staff should be there to moderate the threads being started by the members. And if things slow down, they should fill in with new topics. It shouldn't be mainly staff starting topics.