Actually, it's not clear. There are maps on screen that contradict it, as well as other things (not least of which is the inclusion of inter-stellar travel times in the licensed book).

The "one system or many" debate has been going on for some time on the Serenity RPG board, with people citing "proof" for both sides. So while I'm not saying it's one way or the other, it's certainly not clear that it's one way or the other.

You can go check out the board for the whole discussion if you care -- I've only skimmed it, so I'm not qualified to debate either position :-).