With arcardey physics, wether night nor weather tracks, only 8 cars on the track, no track creator and many more things gt5 will have! Why do you guys ever try to compare forza with gran turismo, they are not in the same league!!
in all truth, FM3 really is the only game in GT5's league. neither compete (released a full year apart on different consoles), but the only game that is even in the same genre as them on their respective consoles released internationally (the elusive "console sim") being NFS: SHIFT. now, we can all agree that the NFS: SHIFT physics, car list, track list (with the exception of spa-francorchamps, a glaring omission from both games) and graphics are up to neither's par, but with FM and GT, both have their drawbacks and advantages. it's a bit of a classic competition in that sense (which is better, 500 average looking, varied cars or 200 great looking cars and 800 bad looking cars with little variation, which is better, customisation or rally, weather and night, etc.)
once again, neither of these games can yet be considered outright better than the other. on both sides, we're left with companies that communicate poorly and games that are both horrible in some senses and wonderful in others. in the end, most people truly in-the-know pick their poison by the console they have. I myself think both games will be great, but I'm admittedly a bit bias towards FM (but I'll be buying GT5 too!)
as for the question of physics, that will have to wait for GT5's launch.