Even though AMD has plenty of 65nm CPUs in the market already and they have proven to be fairly popular, they are still planning to release one more iteration of the older Windsor core. It won't be gaining in the performance arena, with the newest 6000+ unit running at the same clockspeed as the existing units. However, the new X2 Windsor will have a lower TDP compared to the earlier Windsor, down to 89W from 125W.
A significant reduction, but still nowhere near what the 65nm CPUs can provide. While the rest of the X2s have steadily moved over to 65nm, AMD still sees it fit to leave the highest-clocked CPU with the older fab. This is probably a money or resource concern, rather than anything else. It could also mean that AMD is having difficulty bringing their 65nm line up to 3GHz, though I doubt that is the case.
However, since it is the only 3GHz multicore CPU from AMD expected in the short term at all, a power reduction will be beneficial to those who pick up a 6000+.