The problem is that EA/Maxis completely screwed the launch up, due to the requirement that you have to always be online.
And while the enduser might have a good internet connection, he has no guarantee that EA/Maxis' servers are always online.
The reasoning was somewhere along the lines of "calculations have to be done on our servers", "your saves are saved on our servers".
Just recently however somebody released an offline mod for SimCity that works just fine. After that they had to admit that it would be possible to make the game entirely offline. They still decided against it. So if you, or EA/Maxis, have no internet connection - for whatever reason - the entire game is unplayable.
Personally I'm *** that they made Multiplayer without an option for Singleplayer. But I don't even own the game and I hope that EA will get the message.
PS: the reason why I use "EA/Maxis" is because I'm not sure who owns/maintains the servers.