If you want an example of the city build game that has online DRM that makes it look like a service, then look at how Anno 2070 did it:
I hate myself for this, but Ubisoft's DRM actually looks like a service, so developers really did it right with that game. To begin with the multiplayer is real because players play on the same map, there is an offline option and the game will work, however there are plenty of incentives to stay online. There is actually some elements that remind of MMO content like daily quests, mini campaigns that are basically "global events" and even letting players to vote for one of 3 factions for presidency which will give global bonuses to all players in any game.
Of course this credit should go to developers that provide content making the always online DRM tolerable. And... ugh... can't believe I will say something good about them, but Ubisoft gets some credit for actually providing functioning servers to their customers.
So yeah, Maxis failed as much as EA.