I am yet again amazed at people's belief that moving from .15 to .13 um is a reasonably simple change. If AMD had problems and had to significantly revise the athlon from one layout .13 um to another to get speeds up, do you really think ATI can just reuse the current R300 chip design? No, they will have to alter many thing because things like cross talk and stray capacitence change when switching sizes. It won't be worth it. Not with the product lifetimes we are now seeing.
And who really thinks nVidia, after having problems switching to .13 um will help ATI solve any of their problems? That's like saying Intel will help AMD get the .09 um hammers out the door next year. Any help they get for not being first to .13 um will be from TMSC. But TMSC builds the patterns they are given. Things like cross talk between the transistors is an ATI design issue that TMSC can give only limited help on.
Oh, and my source for AMD having two design revisions for the .13 um Athlons was the HardOCP review of the 2400+ and 2600+ CPUs.