Ooh, ya cynic. ;-)
The big "I'm leaving forever! Goodbye!!" type announcements are a bit egocentric though, aren't they? Just slipping away quietly seems so much more dignified. But why leave at all? There are loads of threads on this site that don't involve anything nasty or contentious. If people could only hold themselves back and ignore the troublemakers, they wouldn't find their strange little games such fun. Trolls love confrontation, and hate being ignored. Not always easy, I grant you, but the only way to deflate their egos.