This isn't just a US phenomenon. It probably started in Japan but there's a well established series in the UK - the MCM Expo held in Manchester, Telford and London. This seems to be rebranding as ComicCon. There are also several big residential fan events, Ayacon and Amecon in August come to mind. But in the UK attendance is mostly 14-25 age group so not too many IT professionals (unless like me you provide a taxi service for your children)