I've noticed that as well ironsky,
I'm never sure if they join with intentions of posting and never do, or if they want to have a look more into the 'background' of things which maybe only members can see - in other words just being nosy. It's awhile since I joined so I can't remember what non members can't see. Pete and Fly don't miss much I'm sure and as Pete says they get rid of spammers.
Then of course there are people like yourself who join and move forward to make valuable contributions to the forum