To say that Hulu has more viewers than TWC is misleading. The graph is comparing apples to oranges. The "reach" for the cable companies is the number of subscribed households multiplied by the average number of people per house. Hulu's reach is the number of unique visitors.

Even assuming that (subscribers * average people per house) is a good estimate, unique visitors is certainly not.

If a household has five residents (two parents and three children, for example), and each of them are watching Hulu at home, the parents are watching at work during their lunch hour, and the children are watching it at school, then they will collectively count as 6 reaches for Hulu, but only 2.59 reaches for TWC.