In Original D&D, both players and GMs roll dice. The outside world is represented similar to PCs ('stats'), and the two player role (GM, Player) share most of the subsystems (HD/HP, Saving Throws, etc).
In Apocalypse World only the players roll dice and they have very different options regarding the system then the MC (even the harm system means different things to PCs and NPCs).
This could help the MC concentrate more on his actual job. Also the players usually dont feel the system to be 'too minimalistics/too rules light', which IMHO happens a lot when someone creates a system from GM perspective.
Where do this idea originate from?