Something to think about

In minecraft: Redstone is turing complete, but you can't make something with it that farms crops or mines for you.

I'm thinking about how the simulation works in Animal Crossing.

For those who haven't played Animal Crossing, your character is the mayor of a small village and you spend your time in the game doing all kinds of minigame activities and jobs taking care of the village, and your home. There are computer controlled villagers who go around and do very similar activities that you do all in real time. The time in the game is linked to the real time and calendar in the computer (Nintendo DS, Wii) that's running Animal crossing and there are all kinds of events that are triggered while depending on the time and date.

What I find interesting about Animal Crossing is that the game is simulated as having things happen even when you're not actually loaded into the game. For example, if you leave the game throughout the Christmas season then join the game in the new year, the game simulates what the villagers would have done in the time you were gone - they all have their presents exchanged and they talk about the Christmas events that happened.

What I want to know is how does this simulation work while you're gone? I know for a fact that the simulation doesn't actually run while you're gone but it actually simulates the game from the intervening time periods just before you load the village (the game world). I'm not quite sure about how they would simulate this.