Ferrari in particular as they are KING of merchandising arnt going to shoot themselves in the foot. Personally I do believe it is possible GT5 may have more Ferrari cars and part of that is perhaps they dont have Porsche and focused on Ferrari in particular.
Point I was making was the FM3 even with past Ferrari contract/cars in their previous games dont seem to of been able to obtain a major exclusive. FM2 had what approx 20 Ferrari cars. Those are likely to also be in FM3, then add in the F50GT (PGR3) the California and the new 458 leaves approx 5 or 6 more at a guess. Its also likely some race versions will appear.
GT as a brand does however have a closer connection with car manufacturers, partly because of its world wide recognition with 10 year history. Yet yes indeed we have to acknowledge Turn 10 have been improving in this area and in particular with Audi.
I think by now it's quite obvious that manufacturers don't give any real credence to any game or developer, all seem to be on the open market regarding licensing. Only Porsche have been stung by a long term EA agreement that T10 have managed to 'persuade' to allow them to use.
If anything isn't it quite amazing that PD with undeniably more 'standing' in the automotive sector hasn't been able to translate this into major exclusives?