The models of forza 3 are not 3d scan models.
There's a "real life" measurement of some cars: they put some main lines on the car and they enter the position of the cross points. This is a very accurate method but that is not 3d scanning.
A professional made the 3d mesh with pictures and the mesures... You can easily see on the video of the FM3-veyon that the 3d mesh is more complicated than the stripes they put on the real car... Stripes made a too simple mesh that made appear angles in a 3d game.
Plus... I don't think they use this technic on all car in the game, because it's more, more, more expensive than indian modelers they use.
Don't forget it, in 2010 there's always a human behind a 3d model. Don't forget it when you stole it. ;)