[zheshishei]

In this case, it's more like the Bystander Effect[1], which is related to the tragedy of the commons. Both can be the result of what's called the "Diffusion of Responsibility" [2]. Specifically, the game model this is following is the Volunteer's Dilemma [3].

[1] http://en.wikipedia.org/wiki/Bystander_effect [2] http://en.wikipedia.org/wiki/Diffusion_of_responsibility [3] http://en.wikipedia.org/wiki/Volunteer's_dilemma