Viral videos have a power that partisan media lacks. If a video succinctly makes a point about Bush's record in Iraq, thousands or even millions of people, regardless of party affiliation, may decide to spend a minute and a half to check it out. All it takes is a click of the mouse.
An excellent article in a magazine, however, requires finding a copy and reading for half an hour. Too often, the people willing to make that investment already agree with the article's point.