No comparison unfortunately. The XBox 360 and PS3 are so far behind the PC in terms of raw processing and graphics (memory and texture bandwidth being big culprits). The flying games on consoles have to use various graphics "cheats" in order to render the pretty graphics that they do, but it is far from the amount of data that gets rendered for flight simulators on the PC. Racing games have VERY small enviroments that in most cases are designed by the developers and optimised for good performance. Most flight simulators can display third party custom scenery, and has to inteprate and display anything from vector data for roads, powerlines, rivers and coastlines, land-use data and huge texture sets to cover the landscape, buildings, objects etc.
Even if the next generation consoles will provide the required horsepower to run a flight simulator, there are not that many developers who will risk developing for that platform as the return on investment for flight sims is probably too low compared to racing and action titles. It could very well be that something like MS Flight could probably be ported to a next gen XBox due to its lower level of complexity, only time will tell.