I'm pretty sure they reused lots of Sims 1-3 code, and they really have this simulation thingy figured out. Most probably some really good and generic engine, or else they could not pump out Sims extensions every other month. I have quite some respect for this, it certainly took years.
> I'm pretty sure they reused lots of Sims 1-3 code
You made this assertion elsewhere in this thread also. I don't see any reason to believe this is the case, do you have any evidence in favor of this theory? There's a huge amount of PR from them saying this is not the case, and from my minimal experience with game development it makes no sense.
The same amount of PR of them saying that you need to be online because servers manage these "massive" simulations. No, I have no evidence, would be cool if someone from Maxis explained the differences between Sims and Glassbox. What they say here [1] also applies to Sims, only on a bigger scale. I have yet to see a feature that does not somehow exist in Sims.