from about.com

The morning email alerted me of a new article about "The Sims 3" at CVG. EA talked with CVG about how they believe taking "The Sims 3" into an open world is risky. When I saw the title I thought I missed an announcement about "The Sims 3 Online" being developed. Now that would be risky. With "The Sims Online" being unsuccessful and all.
Two risks they mentioned were the other Sims in the city aging and changing while the gamer played their family. This may make the game easy. The other was the open environment; meaning Sims can walk the streets of the town. Uhh... EA I believe this is something many gamers have been asking about for ages.

I think the real risk here is pushing the date back 4 months. Maybe it's just me, but I make an effort not to anger those who are loyal to me. Plus I wouldn't want to be on the receiving end of a few million ticked off Simmers.

Honestly, the free will can be turned on or off, so it should not be an issue.

it can be turned off? what about the town part of it?

You can turn the town part on/off too. I think it's called 'Story Progression' or something.

The player has the ability to control one family at a time and easily switch from one family to another. All the Sims of the city evolve together, but if you want you can stop the aging or the story progression. In this way Sims that you don't control won't get married or evolve.

But players can pause age progression on a Sim/family which stays on even when you are not playing the family.[13]

The player can choose the length of a Sims life, from 25 Sim days to 1000 Sim days
http://sims.wikia.com/wiki/The_Sims_3

Yes I realize a Wiki entry isn't official news, but it cited with this

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