Flightsim also have to dedicate more power (then an FPS) to a grapichs _related_ calculations. It is obvious, if you can recall, how large visibility range is in any FPS. Max 500m in FPS vs 5-10 km in a flightsim. So, in many cases an average flightsim may have more polygons in the scene, then an average FPS of the same age.