Yet another example of developers treating their customers like idiots and just lieing to them. That explanation of offloading calculations to EA servers is complete bullshit. They said in the AMA that if you lost the connection while playing, you'd be able to play for a couple of minutes before being booted out of the game. Clearly, if EA's servers are performing calculations that are so vital to the efficient running of the simulation, then this couldn't be the case. You'd start seeing crazy behaviour as soon as you lost your connection.
Not only that, but the bandwidth required to keep calculations for individual sims synced up with the EA servers would be crazy, there's no way EA have servers that could handle all that stuff for so many players at the same time. It would be like trying to run servers for an MMO, where every single person playing has up to 100,000 characters playing simultaniously.
EDIT: As Fugitivelama has pointed out, what they probably meant was that the whole region idea is all processed server-side, rather than the sims themselves. This makes most of the above rant incorrect, but the issue of it being completely unneccesary online-only DRM still remains. I certainly think they've been exagerating things when they say GlassBox "attributes portions to EA servers". That makes it sound like your PC works out what needs to be calculated, and then sends a message to a cloud based server to calculate it. In reality, it's much more likely that it's just some server side code that does some stuff before that information gets anywhere near your PC. In other words, it's doing what every other dedicated server based multiplayer game has ever done, maybe with a little bit of extra processing, and they're just trying to word it in a way that makes it sound like the always-online requirement is a necessity. In reality, it's just that either they think always-online DRM is a good idea (SPOILER: it isn't), or they're really shitty designers.
