The ww2f server won't let you post unless your browser identifies you as a specific member. When you click "log out" the server cuts off your connection, so if you return and are able to post, your browser is set to record and submit your passwords. Cookies are used to record your sessions so you won't have to log in every time you post.Automatically being able to post when you get here is not a really a problem unless you are using a public computer. I haven't entered my password for this site for about 3 months now.
Cookies don't actually get removed after a visit unless you set your computer to delete them.