I highly doubt there's any significant calculation. If there was, EA would have to rent hundreds of thousands of EC2 instances to cover the running of the game.
On the other hand, if there's no significant calculation on the server, why would EA pretend they were having massive load problems? Sure, maybe they wanted to get some headlines about 'SimCity is so popular it's having launch shortages', but there's got to be a happy medium between "friendly headlines talking about SimCity's popularity" and "seething EA hatred plastered across the Internet".
I think it was just poor scalability engineering. They didn't expect that many users on launch and they didn't implement a system that could scale upwards.
They knew exactly how many users to expect, I'm sure. But you aren't going to pay for a solution to handle all of them when you expect the demand to taper off after a few days.
I'm pretty sure the server is running some, if not all, of the simulation code, in order to prevent cheating. If they just blindly trust client updates, I can simply send an update that gives me another million simoleons.
And this wouldn't matter that much because it's not truly a multiplayer game. You would be cheating at your single player , non-competitive game... big deal.
