adamj: My understanding was that the second cable was for the new satellite that Sky may be using when it is commissioned next year. There is no need for a second cable for the same satellite
I happened to have an electricican here altering my wiring when the Sky HDi installers came. They said that I may as well get the electrician to run the extra RF cable then, as he was unsure how much SKY would charge to do it sometime in the future, but it was likely to be more then getting the guy to do it now. I did it, but I wonder how they could charge for something it should do out of the box?