Actually this isn't entirely true.
It is much easier to run the stuff on the server side due most of the indepth calculations and simulation portions than trying to program it into self contained program.
Since they made it server based, they were able to ensure the it all works well without having another Simcity 4 problem.
Maxis has openly stated they wanted to do a Simworld/SimNation for Simcity since the release of Simcity 2000: Network Edition with a full online mode.
So this no surprise.
Most computer games now have a form of always on DRM including Steam!
Even if the reason behind always online was that they wanted to recreate Simcity 2000: Network Edition, and not DRM (No way I'm buying that) the always online has obviously put major limitations on what they can do in terms of scale. You take away the online, and your able to match SC4 in terms of scale.
You are right. It's like they wish to improve upon the game but when they revamp the game they take away all the features that made the game in the frist place. Case in point. CSS (Value) reworked this game (now called CSGO) and it's not to say there have been improvements, but they take away the fuction to set the BOT up in offline mode example money weapons and the such. Hell I have spent hours just setting up and playing the God mode and teraforming in SC4 just before actualy playing the core of the game. I tell you folks the new version of SCxL cant even compare to SC4. And all because of this online multi player BS. Look it's a game we Can Have Our Cake And Eat it too. End of Rant.