So this is why it's harder than hell to find 6990s and even 5970s everywhere?
Figures.
Could be the confluence of a number of minor conditions coming together to result in one major outcome (supply not meeting demand).
The Bitcoin mining "fad" is certainly fueling a non-zero demand for 40nm gpu gear that AMD might not have predicted and thus would not have factored into their wafer start allocation models for inventory management (something that has a healthy 3 month lead time after all).
[note: I am referring to
BTC mining as a fad only because of the accepted notion that eventually it won't be cost-effective to pursue mining...BTC's themselves may or may not be a fad, obviously lots of people aim to ensure it does not become merely a fad]
At the same time AMD may well be intentionally ramping down their wafer start allocation for 40nm gpu's IF they are on the eve of ramping up 28nm gpu wafer starts. They have to manage that transition, for their sake as well as the AIBs and resellers. No one wants an inventory overhang when 28nm starts making the headlines.
Demand for 40nm won't go to zero, obviously, but there will be an inescapable immediate reduction in the perceived value of the 40nm gear once 28nm is on people's minds.
Just saying, there may not be any one dominant reason for the supply not meeting demand, but a lot of little things may be adding together here to create the result.
One thing is for sure, when 28nm arrives, owing to its improved performance/watt there will be a sizable immediate demand placed on the GPU's for the sake of BTC mining. Gamers may be left in the cold in a way that will make the supply issues of Cypress and 40nm seem like good times.