Why do lots of TV stations advertise a program for say, 8pm EST / 9pm PST? Lots of channels have East and West versions, but what about those that don't? And those that do, what happens to those folks that live in the middle?
The reason is because shows are broadcast live on the east coast, and tape-delayed for the mountain and pacific time zones. The networks don't have time to rewind the tape to broadcast stuff at 8 central, so they broadcast it an hour earlier.