Randomness on Wiki's

Ok, so wiki's can be a place for collaboration, or just a web site open to editing and comments. I guess I can see the collaboration piece -- it would be a good place to put projects that a ppld team is working on. But much of the ppld intranet hardly seems open to editing, though I guess the team's project would be living there. So I get it -- it's a place where a group can access shared information and add to it and work together on it. Am I right? It was kinda weird looking at other libraries' wiki's. Is ours available to the world like that? I didn't think so. How come theirs is and ours isn't? Or is it?