Sky do sell on the rights to show episodes to broadcast channels. In the past Channel 4 have shown Stargate SG-1 and Five showed Atlantis but neither performed particularly well. Generally, people who want to watch the show aren't going to wait for terrestrial repeats anyway.
Well Channel Five decided to show half of Atlantis at 1 am, so bad ratings arent surprising.
No one should get their hopes up about seeing Universe on Channel 4 either. MGM were not
happy when the dribbling Morons that present T4 decided to take the piss out of SG-1 after each episode.