Shocking, right?
Could it possibly be related to the fact that their CEO Marissa Mayer is an Obama bundler?
Yahoo appears to be out of Kookifornia, so it's not at all surprising that it's bias reflects that of the nuts and fruits state.
I personally think that excessive access to money tends to make people Liberal, and that is why California, New York, and all the other "rich" areas of the country are profoundly Liberal.