just follow the link you posted yourself. that say that people is always connected when playing starcraft 2.
http://kotaku.com/5344013/starcraft-ii-can-be-played-offline
Also confirmed by Rob Pardo(one of the lead designers of StarCraft II) during the Battle.net 2.0 presentation on BlizzCon.
If you got any new information specifically from Blizzard that clearly states single player won't be playable offline please tell me. So far I've heard none.
I'm guessing you're going to try to crawl around and say that there is no guest mode because the button isn't in the beta. Well, actually Blizzard just removed it from the beta. Check the video and you'll see that the feature is still there.
http://www.starcraft2.com/features/misc/battlenet.xml