I don't think any FFs have failed in Japan (even X-2) broke the 2 million mark. Everyone knows FF XIII will be huge in Japan and as a true Nomura game Versus XIII will be much bigger than X-2. Both of those games combined with GT5 will put the PS3 at the very least in the 5 to 6 million range, and due to the fact that no 360 game sells more than a few hundred thousand copies in Japan, when the PS3 has 5.5 million consoles sold in Japan and two million plus selling games to boot, then you will almost all of the Japanese developers that make hd games begin to make almost all of them as PS3 exclusives.
If Yakuza and White Knight Chronicles can put PS3 over the Wii in Japan for 12 weeks straight at its old price, then you know two exclusive Final Fantasies, GT5, and a price cut that brings the PS3 to within only $50.00 of the Wii's price will have a much more profound effect.