Hey! wake up! GT5 cannot sell 10Mil. Even GTAIV, the most popular franchise, far more popular than GT, didn't sell 5 Mil yet. Why a game less popular can sell 2 times more??? It doesnt make sense and I think everybody who believe it will sell 10 Mil believe also PS3 will sell 100 Mil units and that won't happen. Sorry!
Uh, you do realize GTAIV is also availible on the X360, correct? If you include its numbers, it passed 10 million on its 14th week. GT5 is capable of hitting the 10 million mark. GT has always been bigger than Halo, and Halo 3 hit its old numbers without too much trouble (~8mil).
Now, is it possible to hit 10 million faster than Mario Kart Wii? Hardly. First of all, it would have to release simultaneously in all three regions, when GT never does. Secondly, the PS3's strongest region is in others - the land of legs. Take a look at the sales curve of GT4:
I gave it 35 weeks, which is pretty generous (Mario Kart Wii will be well over 10mil by then). By week 35, it only managed 3.2mil, less than 60% of its lifetime sales. Note that this game sold about as well as GT3 in others, so using similar numbers would be the best case for GT5. America & Japan would need to make up the other 6.8 million in 35 weeks... Assuming a generous 20mil installed base there when GT5 comes, Japan and America would need to sell to over 1/3 of the userbase in 35 weeks.
Anyway, in the slim chance it does pull off this miracle, I still think Wii Sports Resort is going to take the crown.