^Why? Sayang naman yung profit gained from sponsor commercials from the broadcast. Some shows did do that (Firefly, Dollhouse, etc.) but only 1 or 2 unaired episodes and only because the network cancelled them prematurely or to provide closure to a story arc while waiting for the network to decide whether to cut them or not. Those episodes were available on DVD as a prerogative of the showrunners for loyal fans. Just correct me if I'm wrong.
From what I've read, it was NBC who ordered the extra 6 episodes and not an initiative by the showrunners.