Aha! Physical fluids aren't Naiver Stokes, which is just a continuum approximation that was invented before atoms were even a scientifically established idea. Which of course you know already, but it means it is begging the question a little to say "you might be simulating something but it sure ain't a Navier-Stokes fluid".
For Galilean invariance, I've previously waxed philosophic about why I think that's a feature, not a bug (at least, pedagogically): http://news.ycombinator.com/item?id=5931434
For Galilean invariance, I've previously waxed philosophic about why I think that's a feature, not a bug (at least, pedagogically): http://news.ycombinator.com/item?id=5931434