Disney’s entrance last month into the Hulu fold marked another milestone in the young online-video service’s short history. The implications of the deal, which will see Disney TV shows and movies appear on Hulu for the first time, are serious and far-reaching. But the most obvious is that three of the four major US networks are now part of the service. If there were any lingering doubts that Hulu deserves its seat at the head table of US TV, they are now gone.