'web' apps are expected to work on the 'web'. It kind of goes without saying that it there is no network it can't make whatever calls it needs to in order to load data.

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.