Some of the stars may not want to do TV.
Anton Yelchin has been positioning himself for a while to be the "Next Young Movie Star" with films like the upcoming 'Charlie Bartlett'
. Zoe Saldana is starring in Twentieth Century Fox's "tentpole" movie for 2009 -- James Cameron's 'Avatar'
. I think at least those two want to concentrate on films, and not be saddled with TV commitments that will take up too much of their time. When you commit yourself to a TV show (you are usually contractually commited), it is sometimes very difficult to find time to make movies. I also have the feeling that Urban and Pine would rather do Movies than make the TV-series commitment.