"Throw in the towel" is a rather harsh and perhaps knee-jerk characterization of a plan whose details have not been illustrated or announced and probably won't be for at least a year-and-a-half.
Also note that the "10 years of war is enough" statement in the article is the reporter's editorializing, it is not something that Harper said. A somewhat better version of the story can be found here: http://www.nationalpost.com/news/story.html?id=782446
I wouldn't be surprised to see Harper announce a major surge (by Canadian standards anyway) after he is re-elected to achieve the Coalition's goals in Kandahar by 2011. Also, given his government's large investment in and restructuring of Canada's special forces (Special Operations Forces Command), it wouldn't be surprising to see a significant contribution by Canadian SF in Kandahar and elsewhere in Afghanistan post 2011, perhaps in a bit of a role-reversal with Australia.
Keep in mind that Harper orchestrated some brilliant domestic political maneuvering to extend the Canadian mission from 2009 to 2011 in the first place. He has a history of promising little and delivering much.