Yes, the Sandy IGP is probably "good enough" for most users, and with the end of production for the C2D, Apple really didn't have much choice without a pretty major redesign, but that doesn't lessen the sting for those who were hoping for something a little better.
If you read the benchmarks carefully, you will see the the 320m actually outperforms the Intel Sandy IGP by a lot - 30 - 50% in more GPU-intensive games and settings. Stands to reason - the nVidia IGP has 4 times as many shaders and better drivers behind it. The Sandy does get a higher clock and more memory bandwidth, but that isn't nearly enough to close the gap.
As for me, as soon as I heard "Sandy Bridge IGP" in connection with the MBP 13, I ordered the 2010 model (and happy I did, as the C2D can do anything the i5 can do - if only slower - and the 320m can do some things Sandy can't, like OpenCL, CUDA, some games).