Unless you bought Portal on Steam and didn't sign in when you had an internet connection.
The DRM strategy in Sim City is not the same as Steam, and cannot really be compared. EA are forcing unnecessary always-online features into what most people expect to be a single player game, preventing it from being played offline at all, in a thinly veiled attempt to prevent piracy and resale. That would be bad enough, but what makes it utterly unacceptable is that they haven't provided the infrastructure to support it in the short term, and clearly don't have the business model required to support it beyond the first few years.
Why anyone would knowingly support this business practice at all is beyond me, let alone for a game which has had such dubious pre-release reviews and is now essentially unplayable.
Games are not generally expected to require a network connection. If I take my laptop to the coffee shop without wireless I can still play Portal and Anno 2070.
Not so with the new SimCity.
Not to mention, there is an expectation that if you buy a game (especially on physical media) that you will be able to play it so long as your hardware supports it. I can still play Quake 3 for example.
With SimCity, if they ever shutter the servers or sunset the Online Service your game becomes nothing more than a pretty coaster.