Yeah, buddy of mine who used to work for GW here on the east coast assures me that typically GW has things done WAY in advance and just like any other company, has release dates (which are subject to change) which has the side effect of keeping army/product loyalists chomping at the bit forever (until we abandon hope and move on to greener pastures). Then, by then it's too late.
Key point in economics* Demand to Supply ratio: Butt tons of people screaming for a Tau codex (which can probably be heard on the moon) + arbitrary zero fulfillment of market demand by production company = 0 profit from market. I'm sure Keynes is twirling in his grave about now.
This is why I've shelved my Tau and will be concentrating on my guard forces; or even a whole new gaming system.