The reason why it's set up like that is because it means all the permissions are the same regardless of the User Group (besides for Admins), which means I don't have to manually adjust the node for every staff User Group and if we make any changes to the staff User Groups I wouldn't have to manually update every node's permissions.
On .org their User Groups have been static for a while, but we have a LOT of staff specific ones, including a new one for every Sub-Moderator category. So it's just easier this way, at least for now. I don't want to run into future problems where permissions start getting broken. It's just more "scalable" that way for now.