This might
get me crucified, but I think one of the biggest reasons GT5 got
delayed (I know, there was no fall 2009 release date, but you know what I mean) was because PD saw the feature list of other racing games and decided they needed more work. I have no doubt that what they had was beyond anything in the competition, but they might have decided to add other features which were missing in their game.
And that, IMO, is an excellent thing. Why not make your game better if you can learn from something else on the market? In India, we have a saying which goes like this, "Never disregard even the lowliest person, because you might learn something from him which you didnt know already." That seems like a very good philosophy to have.
I think PD is going to break the genre of sim racing with GT5... with such a long development time, I think they are going for broke and will do exceptional things to make GT5 the next gen racing game to end all next gen racing games. And anything which makes them push for excellence is good for PD, is good for its consumers and is good for the racing genre in general.
EDIT: I am not trolling GT5, or extolling Forza or NFS:Shift, I am just trying to think of some reasons why the GT5 release date might make sense. If they are truly going for something exceptional, and beyond anything else on the market, why would they not go for broke? I applaud them for their dedication and commitment to make GT5 the best it could be.
I just wish it had released earlier, and other things might have been patched in, but if this is how PD thinks GT5 might be best enjoyed by me and millions other customers who are waiting with bated breath for what is sure to be an excellent game, then I am more than willing to extend my patience for 3-6 more months. More power to PD... I hope they ship a game with the kind of scope they have in mind.