Re: FTL...
I don't think there are no ships with FTL. Just that the Serenity (Firefly class ship) is an intra-steller vessel, without FTL. There are probably intersteller vessels with FTL, but those probably belong to the Alliance (and were the means to reach this system in the first place.)
Think of how our ability to see planets in other star systems has progressed over just the past five years. Assume it becomes even more precise in a couple hundred years. I mean, if you view systems from a distance and can pick and choose where to set up a group of colonies, this unique system would be ideal, especially if FTL were possible but not practical to maintain governance over colonies scattered across multiple star systems.
It might even be that there is no FTL, and this system was reached by travelling near-light speeds (taking several years), making a system like this, with a high number of terra-formable planets and gas giant moons, an even more logical choice.