Polyphony Digital have published a list of all the Gran Turismo games to date on their website. Nothing exceptional about that you might think, but they have included the sales-to-date for the games in each region.
One interesting trend is that the American share of sales of GT games has fallen in proportion to the other regions. The original Gran turismo sold almost as well in America (3.9m) as it did throughout Europe (4.6m) and more copies of GT2 and GT3 A-spec were sold in America (3.9m and 7.1m) than here in The Old World (3.6m and 5.8m).
In contrast the number of sales that the GT4 and GT5P editions of the franchise have seen in the US (2.9m and 0.7m) have paled in comparison to those in Europe (6.1m and 1.8m) with Europeans buying more than twice as many of those titles.
The series has racked up impressive lifetime sales across all editions and territories of just under 52 million copies. 52 million! No wonder Polyphony Digital can afford to take their time getting changing weather and crash damage into GT5 before release.