Asheth, actually the gap is closing in slowly, now with the PS3 slim coming out it might even get closer, but Microsoft already has an ace up their sleeve which they are about to drop soon (remove one console and lower the top console price to 299).
Real numbers currently:
The PS3 has slowly been eating away at that 10 million gap over the past 6 months. The 360 beats it in overall sales each month, but by less each time.
Now on the point about Forza v. GT5, the GT series has always been the premier driving simulation. Yes the AI has been below par, the cars do not get damaged, but in terms are accuracy and precision the GT series is still number one (based on GT5p and what information we know of Forza 3). Now with the full GT5 comes out and Forza 3, we will better be able to determine the higher power.
Those who try to argue a 360 v. a PS3 are just hurting themselves. Each one beats the other in one category and loses in another. The PS3 has the
potential to have better graphics, but Sony limits itself by out casting developers and game studios with no support for the system which leaves them finding their own way to make the game. Also, (not sure if they lifted it yet) studios who develop for the PS3 cannot share "developer kits" with other studios to help each other when developing for the PS3, per Sony requirements.