this explains a lot

Students who thought of Superman volunteered much less of their time than those who thought about other superheroes. Furthermore, Superman-primed subjects were significantly less likely to show up at a meeting for volunteers held three months after they were initially asked to participate.

The reason, believes Nelson, is that asking people to compare themselves to an exceptional individual makes them realise their shortcomings. Whereas thinking about a general category encourages people to identify the strengths they have in common.
-- New Scientist: Superman too super a role model�