I'm not sure if that's true...about the Warmachine decks. They had decks for "mark one" that were the entire set of cards for whatever faction. The released second decks when Mk. 2 came out (they actually gave stores a long card box with tons of mark 2 cards to give to people buying models on the shelves that had old cards in them as well).
I just believe that decks of advantage cards, alone, is a viable product. Decks with character stat cards is probably slightly less viable, as you rarely have need for character cards you don't have the figures for. But a deck of advantages would make me go "whee!" as i wouldn't have to buy 3 of the same figure to get "legal" (as opposed to proxy) advantage cards.
But Privateer only releases Faction decks for models that have been re-done. AT has yet gone through a revision, so a faction deck would be unnecessary to say the least.
Conversely, if they released game aids like life point counters or state counters (More permanent ones as oppose to the ones from the starters) I would instantly buy those.
Of course, I'd love a Saga I & II advantage deck. If they gave me three versions of all advantages from that saga and sold it for 20 bucks, I'd be down.