What makes GT and Forza racing sims, what disqualifies GRID from being one?

[Mummelmann]

To be fair, Forza and GT might be console sims but I don't see them as fully blooded sims. It might be the somewhat cardboard feel to driving on those games (Haven't played GRID so I have no grounds to compare) or it could be my wheelie run at 2900 km/h with the Escudo on the test track.
Who knows?

I'm a good driver in real life but there's no way I can pull off the maneuvers I do in for instance GT, in real life. The cars just don't respond the same way at all (yes, I've tried some fairly crazy shit in real life).