According to our sources, it seems that NVIDIA is using a sort of "Contra Revenue" (NVIDIA calls this strategy “Laser Program”): its partners are selling GTX970/980/980Ti at lower prices than usual, so NVIDIA will refund partially these losses. This happens because NVIDIA has moved up Pascal commercialization and its partners weren't ready (they have to clear their stock).
For example, NVIDIA will refund 125$ for each GTX980 sold, 100$ for each GTX980 and 75$ for each GTX970. This explain the exceptional discounts at EVGA US store, where you can buy a 980Ti CLASSIFIED GAMING ACX 2.0+ for just 339 dollars!