To give a sense of scale to the development time, the list of things that have taken less time than Duke Nukem Forever: http://duke.a-13.net/
This includes the space race, from initial challenge to actually landing on the moon.
This includes the space race, from initial challenge to actually landing on the moon.
The two Mars rovers, Spirit and Opportunity were proposed, authorized, announced, designed, launched and successfully landed upon Mars where they have been exploring the surface for over 2.5 years.
>The United States' entire program to put a man on the moon, from Kennedy's challenge to the landing.
So, it's even worse than that list implies.
Off the top of my head, two additional games in the main Final Fantasy series have been released, as well as The Sims 3 and The Sims Medieval, the Nintendo 3DS was released, it goes on and on.