You guys can't blame nvidia for this one
Apple purchases the chips straight from Nvidia and ATI to make their own cards. Don't believe me? Call ATI and Nvidia.
When the 9600xt and 9800xt weren't clocking as they are supposed to be on pcs I called both apple and ATI. Ati mentioned that they don't support what apple ships in the macs because they don't produce the whole card. They only produce the chips. Nvidia is the same way.
So, blame apple for not producing the cards not NVidia. I'm absolutely sure NVidia has plenty of 6800 ultra chips. Just look at how many different 6800 ultra versions there are.
I agree the g5 chip yield is definitely out of apple's control. Which is understandable... but why announce a product when it isn't ready. I feel they lose just as many customers as they would if they didn't announce it and waited until it shipped. It only hurts their stock and reputation in the long run by pre-announcing products.