We also make maps of the Earth. They tell us useful things, like how to get from point A to point B. But nobody mistakes a map of the subways in New York for riding a subway.
Sure, but that isn't simonh's point. Those simulations aren't very good. There's nobody living in those simulations that thinks that they're alive, let alone that is capable of creating a working computer out of the material in that simulation.
Right, and the Billiard Ball Example shows what you need to do to even just simulate a game of billiards. To do so accurately you have to simulate every elementary particle in the observable universe. That's how complex and interconnected the universe is.
Arguing that present technology is insufficient doesn't prove that all future technology would be insufficient. The trajectory of improvement rather suggests the opposite.
It's not a matter of technology, it's a matter of complexity. By definition a computer capable of simulating every elementary particle in the universe would have to be many orders of magnitude more complex (in crude terms 'bigger') than the universe itself, even assuming ideal technology with mathematically perfect efficiency.
and we create the simulations with the rules of the "real world" that we know. So we can study also the interactions of the rules that we know. But not what we don't know of out universe.