I think Gizmo is correct. The part he left out is.
When deleting a member depending on how you do it.
You have a option to delete a member but leave the posts intact.
So the posts from that member become member 1 (anonymous).
If that makes any sense.
So if you opt to delete the user and their posts yes they are gone completely.
Also if you allow guests to post, even if they can manually post their name they become member 1.
Just believe me you don't want to go down the road of being member 1 for a vanity reason. It would be a modification to the stock code.