News is feed to us on the basis of what we are offered, not what we ask for. We can choose not to take an article, but we do not ask for articles. When we feed news to others we have choice about what articles we send them - again they can reject these if they choose.
The protocol used for news is called NNTP. You can ask for articles with NNTP - and this is how news readers without direct access to the spool disks work. This is not our primary method of reading or recieving news.
Innd doesn't deal with users posting news, cleaning up or even the sending of news to others. If innd thinks you are a news reader ( and not a feeder ) it connects you to a nnrpd. Cleaning up is delt with by news.daily, which is run from cron. Newsxd aranges for the news to actally be sent.
Posting of news is done via a program inews - which is sgid news, so that it can read the authinfo needed to post. Netscape can read news via NNTP, though it cannot post, as it isn't able to use inews.
People can run ( say ) nn on another machine, and build their database via NNTP. This just requires read access to the server.