If the 'world' in Angel Beats is supposed to be purgatory, technically, why and how is it controlled sejak computers..? And what exactly, are NPCs? It would make sense if the world was a game, like in '.Hack', but it's supposed to be the after life :O

But its not the after life and thats the point. It was created, as the in-between for people with bad first lives. So it was created meaning that leaves many possibilities of how open. And that's part of the charm associated with the series that even though it does not answer the 'questions of life' it still jawapan the character queries and gives them a fulfilled life.