Despite the fantastic performance offerings of the G80 based Nvidia cards, the units are selling poorly. The 8800 cards are industry leaders in terms of features and performance, which includes DirectX 10 support, crucial for the upcoming Windows Vista. Unfortunately, whether due to the higher price point or the low penetration of titles requiring that much performance, or perhaps even the lack of Vista's availability, the cards are simply not in demand yet and it seems that Nvidia will already have their successor lined up before they do become popular. The G84 and G86 revisions are due for release in the first quarter of 2007, which is the same time ATI's DirectX 10 compatible R600 series GPUs will be made available.
Likely, with the release of Vista around that time, interest in DirectX 10 cards will be much greater.