Well I'm sure they'll work in lots of nods and references to events happening behind the scenes (which is how they did it in the OT, and that all seemed to work out pretty well). Plus after the prequels and TCW I think we've spent more than enough time dwelling on the politics of the SW universe.
Besides, I wouldn't be surprised if these characters end up shaping events down the line, or influencing things to some degree. I'm sure the writers are intending them to be more than just a bunch of random nobodies.
And maybe the writers are hoping the show will be successful enough that they're saving characters like Vader for later.
This way, if the show is canceled early on, people won't care as much.
