I'm not really sure why NVIDIA changed its naming scheme again, but perhaps it's to point out that these chips have DirectX 11 support, while the currently available GeForce 300 series chips are limited to DirectX 10.1.
Fun Fact of the Week: GeForce GTX 480 and GeForce GTX 470 will be the names of the first two GPUs shipped based on our new GF100 chip!