Yea, you're absolutely right Sy...they're not required by most lists.
But, the purpose of the exit link isn't really to generate revenue. The purpose is ostensibly to provide an exit for surfers who are either not of age, or stumbled onto porn accidently (yea, right!). The mindset being that providing a way for surfers to exit (much like having a warning page)...shows the webmaster is attempting to protect those that shouldn't see porn.
Realizing the link is a traffic leak is why many webmasters use some minor mainstream revenue generating item. Hell, I had GIANT fishing lures on mine for a while
Almost forgot...I heard from a little birdie that warningpages may be looking into the trapped back button issue
