Looks like the game was three days late and missed it's window for replication which caused the delay. During this time it's apparently really difficult to get time to author BluRay discs and by PD missing their window they had to delay the game many weeks so they could make enough copies.
http://www.gtplanet.net/gt5-missed-p...nes-new-dates/
The other story is that the reason it was delayed three days was because they had to move from SDK 3.40 to SDK 3.50 because of the security vulnerability and the worry that people would be able to pirate copies of the game.
http://www.gtplanet.net/ps3-firmware...ismo-5s-delay/