At the same time, AMD could not spare two sets of engineers and make two chips for two fabs. While this would have definitely been the best course of action, AMD simply doesn’t have resources for something like that.
The big issue is that Nvidia has more attention from TSMC, since it is a larger customer, but TSMC will give AMD as much attention as necessary. If they are both on time, you should see some 28nm graphics chips before the end of this year.
28nm means more transistors that are smaller, have better thermals and of course more graphics power. Next stop for AMD is to make this new core work with its next generation Fusion core, that is expected at 2012.