I personally have never understood our nation's obsession with England's Royal Family. I'm more worried about the monarchy forming here.
It's mostly grist for the media circus. Other people in England (this, for example, is from London's Daily Mail) report on it so the American media can pick up the tidbits for free. It makes good human interest fare.
But I don't think very many Americans (or Britons, for that matter—George is already the one in line for the throne) care that much about it, either.