I'm sure this has already been mentioned, but the PS3 sales are simply not good at all. It seems that people are moving away from it much sooner than I would have expected. That along with GT6's sales makes it apparent that the PS3 won't see the type of longevity the PS2 had.
In fact, it seems just about every 1st/2nd party game has severely underperformed outside of TLoU and Beyond.
The ps2's longevity didn't come from the US.