“[Led] by current shows like Glee, 30 Rock, and Entourage, TV seems to be in a sort of guest-star golden age.” And it’s not just existing television celebrities like Neil Patrick Harris, Judge Judy or (occasionally) Oprah; it’s movie royalty such as Matt Damon, Julia Roberts and Javier Bardem. Even Al Gore has turned up on 30 Rock. Kevin Fallon offers five theories as to why the A-List is itchin’ to get onto the small screen.