It's fake. You know how I know? At the beginning of this generation when everyone complained about the $60 price point, MS promised that games published by Microsoft would be $50, not $60. That would include Forza 3.
And yet Forza 3 is listed as $60 on that site. Either MS isn't good for its word, which I doubt they'd lie that blatantly because people wouldn't forget, or the info is fake.
Putting a racing game on two discs is nonsense. The system doesn't have enough memory to do store a significant portion of a DVD in memory before swapping to another disc.
Also, Forza is better than Gran Turismo. The only people who seem to say otherwise haven't played both. I have and it's not even close. Gran Turismo isn not even a racing sim, it's an arcade game where you bump other cars and the physics are a poor approximation compared to Forza.