Triggers arguement holds a lot of weight with me actually.
Take into consideration the level of advancement of Zion itself. It is a technological wonderland (albeit a touch primitive in culture). This Indicates a lot of time and resources to salvage parts and construct. Now in that there are only 23 people (by the architects own admission) to be reawakened when Zion is destroyed there cannot be enough time and people to completely rebuild to the level that it is currently at.
The new Zion couldn't be placed at the site of the old Zion, purely for the fact that with the amount of drilling and destruction the caverns that were created to house the inhabitants of Zion wouldn't be able to withstand the 6 attacks indicated (can anyone say "swiss cheese"?)
It makes more sense for the machines to create a construct that to all intents and purposes is a wakening from "The Matrix" and allow sentinel programs to tackle the rebellious of the human race, rather than risk the source of their existence.
my 2p =)
Just a coupla thoughts anyway.
*edit* also seeing as Neo is supposedly realeased in 2184 i think it is and the Matrix was supposedly created in 1996 i think it was said in the first movie that doesn't allow enough time for 6 Entire generations of Neo and Zion to grow
