There have been so very many reasons to tune in each week to “30 Rock,’’ but for theater fans the show has offered a special treat: the chance to see some familiar Broadway faces.

Tina Fey’s NBC sitcom has tapped into the energy of the city where it’s set by casting guest roles with some of the leading lights of the stage — an organic fit for a New York TV show about a New York TV show that’s also about the theater.