[Mylon]

Yes, it may have taken America 300 years to get where we have today, but also consider:

1) It isn't a set thing. You can't say 300 years alter America has finally achieved "cultural center" status. Whos to say they didn't achieve it with the invent of the automobile? Or the railroads?
2) Production is skewed by the fact that only one thing can be produced at a time. Such infrastructure as a city doesn't spring up overnight, but it also isn't the only focus of the people.
3) Cost is also skewed because colonies are self sustaining in nature. True, America has maybe consumed its own weight in organics, but sustaining the colonists is free in SEIV because they produce enough naturally to take care of themselves. It is production facilities or other things that cost extra.
4) They're also evolving things. It would be reasonable that if a new mining technique is discovered you shouldn't have to build half of the cultural center over again just to refine one part. The 50% cost factor may be unavoidable, but the tremendus cost of that very 50% assures that it will never happen (assuming multiple levels of cultural facilities).