The Compete numbers are measures of 'people', which in our world = unique visitors. I think the point they are making is that social networks and social media sites are attracting nearly as many people as well entrenched internet brands. For example... A similar analysis could say, "50M people visited a gas station last week to fill up their gas tank. Interestingly, Starbucks estimated it served 70M cups of coffee to 40 million people the same week. It seems Starbucks is nearly as inseperable from the American lifestyle as large automobiles!" I made up these numbers, but the point is that the disaggregation of media is changing where we go and what we read.