Thinking Allowed on Radio 4 today covered this quite well, albeit indirectly. It suggested that while in the past these sort of obsessions (David Cassiday, Bay City Rollers) would fade in the late teens nowadays the internet allows general communication and social networks to build and reinforce such fan bases to the extent that they can self sustain and go on for a relatively unlimited period of time.
(, Wed 30 Jun 2010, 22:14, Reply)