I want to start by saying that Destiny is not delayed. It will still launch on September 9th.
It wasn't supposed to, though; Bungie's shooter was originally set to release early this year. However, it was delayed, a decision that has been deemed a correct one. Activision's CEO Eric Hirshberg said the following on the matter:
It was the right decision to delay it because you never get a second chance to launch [a new game] and make that first impression. Obviously we wanted to prioritize getting the game right and setup for the 10 year vision that we have for 'Destiny.'
Hirsberg also said that he didn't feel like a holiday release would conflict with Activision's mega franchise Call of Duty, calling out the differences between the two games: one is a military shooter and the other is a fantasy/sci-fi shooter, calling out to two completely different crowds.
Just remember, folks. There's nothing wrong with a little patience to ensure the quality of a product. Let's hope this rings true for Destiny.