I heave heard speculation that Nvidia is unhappy with XFX for making ATI cards and that is wasn't just XFX unhappy with the 470/480.
There has been loads of speculation about NVIDIA and XFX in the past, this is nothing new and I sincerely doubt it had any implication on this decision. XFX had retail boxes, artwork, and everything cooked up but simply decided to pull the plug at the last minute.
Given XFX is the only GPU manufacturer to offer a double-lifetime warranty on their products, they may have decided it wasn't worth the financial risk. XFX was a big name when NVIDIA launched the G80 (which is larger than Fermi, btw), so they have prior firsthand experience with large, hot GPUs.
Edit: Rob will probably kill me for this. Speaking of hot,
here's a Tri-SLI review of the 480.