So GT5 is the lowest selling in the GT series so far? That's what the chart in the link says. I know GT5 only shows six weeks and the rest are lifetime, but it would appear that the Gran Turismo series has lost some following over time. Because of Forza and Need For Speed?
GT 10.9 million sold
GT2 9.4 million
GT3 A-Spec 14.9 million
GT4 11.2 million
GT5 6.4 million
63.1 million total copies for the series if you count PSP, prologues, etc.
As Kaz said its a marathon and not a race when he was asked if he could continue to provide support for Gran Turismo 5 post-release.