This trope may be an expression of LoliconAndShotacon. It is certainly related to whatever cultural elements contribute to the fact that you can buy used girls' underwear in vending machines in Japan. (Or used to be able to, until it was outlawed around 2004.) This practice was referenced in (of all things) a 1995 [[http://en.wikipedia.org/wiki/Pulp_%28band%29 Pulp]] concert video, in which it's suggested that it wasn't quite as widespread as commonly believed.
If you want to really psychoanalyze it, you might venture to suggest that the anime PantyThief is an embodiment of the suppressed desires many adult Japanese males have about a) young girls and b) bucking social pressure and the forces that make them behave "respectably." Or it could just be another expression of the fact that going against social mores produces good comedy.
-- jkbeta, moved over from the trope page (12th June 2012)