Quoth Moore and Eick:
"This show was always meant to have a beginning, a middle and, finally, an end," producers said. "Over the course of the last year, the story and the characters have been moving strongly toward that end, and we've decided to listen to those internal voices and conclude the show on our own terms."I think most of the hardcore fanboys and girls knew this was coming. Moore's been talking about finality a lot lately, and when the fourth season order was originally 13 episodes, there were reports saying that if it expanded to 22 -- which it eventually did -- that would be a sign that the Sci Fi people were giving the production team a chance to wrap things up.
So go create a kick-ass final season, guys. Better to tell the story you wanted, in the way you wanted, and give it a proper ending, then to drag things out forever and ever.