The Developers give you the OPTION to either :

Grind your way trough the races and earn enough money payouts (that are not gimped) . to buy said car .

Or

Pay and get the car right now .which could be an option for people with limited time to grind their way through it .

In theory, this would be just fine, but I simply won't believe it until the game has been released as it seems too tempting for developers to increase the grind just to push people into spending real money.

Interesting. People seem to be excusing this a lot more than Forza.

Again, that all depends on how the final game turns out.

Forza 5 was absolutely compromised as a result of this setup. It's entirely possible that GT6 won't be ruined by this but we simply don't know yet.