i don't think you have a proper grasp on the concept. You just don't understand people the way i do. Its like reverse psychology. You put something in big red letters followed by the disclaimer/test forcing them to read it without even thinking about it. How do you think Advertisers get you to stare at the Idiot box every night in between scenes of Operation: Repo. it takes a certain technique to get someone to read something subconsciously. For instance Operation: Repo and most drama/reality based tv shows get you to sit through ads subconsciously by breaking the scene at key moments. its the same concept really. the user finishes the registration and is all ready and eager to get into the forum and the big red text appears, subconsciously drawing them in. it atleast gets there attention, long enough to leave a subconscious awareness. call it a subliminal message if you will.
You're partially right. Advertisers get people to sit through commercials mostly because people don't want to miss what happens next in the show. What they do is, make the ads as long as they possibly can without giving the victim time to do something else. This forces them to sit through the ads.
Also, people fucking hate advertisements. You really want to add something that's annoying like them as a prerequisite for joining the forum?