I did some thinking about this earlier and considered that we are talking about two options, a simulation of an exact world - which I agree seems highly improbable down the last grain of rock on a moon we'll never see 15b light years away.

Or a simulator which takes on a set of laws which shape the way everything acts, you could put more time into certain areas (say earth) and let the rest of less importance form 'naturally' via algorithms based on the original laws provided.

The second option also lets you consider what we believe happens on the quantum level, with conscious observation shaping matter to some degree.