Nvidia partners have high hopes that the company's GF100 / "GT300" / Fermi chip will end up as the excellent seller many enthusiasts have been hoping for and have already ordered some huge quantities of it.
The reasons behind such risky decisions is quite clear. The GT200 family is not as widely available anymore and it seems probable that someone at Nvidia messed up with 55nm wafer orders. We assume this mainly because Nvidia didn’t expect to have such strong demand in Q3 and Q4 and therefore partners are hoping that Fermi can remedy the situation.
On another note, supply partners have to be the early birds with their orders because once Nvidia shows its Fermi supply to the entire seller market, the waiting line to get chips might already be too long. It is not that Nvidia partners have much of a choice though, as the GT200 series is slowly being discontinued and Fermi is supposed to fill the gap.
Nvidia and its partners believe that Fermi should destroy Radeon HD 5870 and HD 5850 sales, but this is only after it starts shipping. Not to mention, this strongly depends on the supply quantities that Nvidia can deliver. Until then, ATI will be making quite a lot of money on its 58x0 and 57x0 series.