Ok, I'm not sure if this has been mentioned before, but take a look at this:
Gran Turismo 4 “Prologue” - 0.410 Million 2004/05/26
Gran Turismo 4 ---------------- 6.410 Million 2005/03/09
Gran Turismo 5 “Prologue” - 2.440 Million 2008/03/28
Now, this is for Europe..
Take a look that GT4 Prologue sold very bad, considering what GT4 sold.
I hope that GT5 makes GT5 Prologue sales look bad aswell.. :)
But WOW GT5 Prologue has sold A LOT..
http://www.polyphony.co.jp/english/list.html
I think GT5 Sales will be REALLY great, the best of the series. Like myself, I think a LOT of people have been skipping the Prologue, and waiting for the full game.. I don't really think a "Demo" or Prologue is worth buying, when it's not even the full game, and I'll either way have to buy the full real game later anyway.. I think a lot of people have thought so. And GT5 WILL get heavily advertised, and it will probably have great bundles.