I found this article interesting as I read it while working on BattleFingers (http://www.voyce.com/BattleFingers) an iPhone game that relates to the social and physical aspects you mention. The basis for the game was the visceral thrill of the track’n'field button-mashing genre, combined with the appeal of having two physically proximate players in a social setting. It uses blunt interaction mechanisms rather than the iPhone’s usual fine-grained controls, making it suited for environments where motor-control may be compromised. The aesthetics and mechanics are deliberately stripped down to the bare minimum, not even having the ability to play against the CPU as being “mano a mano” is so fundamental to the appeal.

Or maybe I’m just over-intellectualising it…