I could be wrong, but I believe the whole September 2008 date started getting mentioned due to the original deal when Sportsnet took over for Prism and the length of the contract. However I don't think it will impact anything as long as they continue to be broadcast by "terrestrial" means. Remember the FCC actually gave CSN Philly an exemption from having to be offered as part of the Adelphia deal.
Comcast must figure that their subsciber losses in Philly would far outweigh the amount they could negotiate from the satellite companies. They also don't want the embarrassment of people leaving their "home" market in droves.
Anyway, I hope I'm wrong and they are forced to offer it soon.