Here's how I see things:

 Gran Turismo 5 Prologue was released about two years ago right? The main game, Gran Turismo 5, was supposed to be released in late 2009. I don't know if you guys remember but there was thread on this site last year about GT5 been delayed to 2010 because of updates to GT5:Prologue. I think that's stupid on Polyphony Digital's fault. They shouldn't be worry about making updates for a preview of a main game. It makes no sense. If they had just concentrate on working on Gran Turismo 5 instead of the Prologue, Gran Turismo 5 would've been out in Japan by Christmas of 2009 and early to mid 2010 in US and Europe. It explains why the game is 65% done. How can a game,that has been in development since 2005, be 65% finished? I understand that its a huge game and it cost a lot of money but thats really no excuse. They could of spent time working on the game more instead of updating the prologue.

This is definitely going to effect their sales. WIth Forza 3 set to release in the coming weeks, by the time Gran Turismo 5 is out in the US, Forza 3 would have proably sold 3 million copies WW. I think this is a bad move for the developers who made GT5 because the game will be 6 months or so behind Forza 3's release. At that rate, by the time GT5 is released, it would take probably 4 months for GT5 to sell as much as Forza 3 sold within its first two months of release. Although it really depends on GT5's first week sales worldwide which is predicted to be huge.

What are your thoughts?

Who's to blame? Sony or Polyphony Digital?

How much time would this honestly take. They work on GT5, then take some of those features and add them to GT5 prologue. There is presumably not a single line of code in GT5P that isn't in GT5. Now what may be correct is that it would've been released by now if it weren't for GT portable

I honestly don't think there should be a Gran Turismo portable. Its just a waste of time. The developers have wasted so much time on pointless updates and trying to make a portable version of the game. They probably wanted to make a portable version of the game to improve the PSP's dry library of exclusive games. Do you notice how most of the huge titles on playstation are now being made into portable versions of the games? Think about it Final Fantasy,Metal Gear Solid, Little Big Planet and now Gran Turismo. Its obvious Sony is trying to dust off PSP's dry library of exclusive games.

Uhhh...they did almost nothing to GT5:P, they added like 3 cars I think and a bunch of small stuff. I doubt this had any affect at all.

And what's wrong with Sony doing that? For ages they've put the majority of their effort into the PS3, now it's the PSP's turn for a while

I remembering the developers of Gran Turismo 5 saying they deleayed the game again due to working on updates for the prologue. Just hold on, Let me find the article.

Uhhh.... this doesn't seem like a good reason at all...

They are wasting their time trying to put effort on the PSP. Btw, they just started putting effort in pushing the PS3 when you really look at it.

they also have more than double the amount of cars than forza
and 1080p in resolution 60fps twice the amount of cars in game.
they were also working in GT PSP. (800 cars)- more than GT4.

just one studio, head by a perfecionist. GT 5 delays are always a given.

maybe updating GT5:P is part of their further experiment with the technology before making GT5.