BootDaily had an interview with NVIDIA's VP of Content Relations. Here's a snip:
BD: In your eyes, which API do you feel is more adept?
RT: I like the features and streamlined programmability that DirectX 10 offers. DX 10 will allow developers to make games that deliver a deeper level of emotional involvement. They will be so realistic that they draw you in like a good feature film.
For example, until now faces on characters have been a big challenge. Have you noticed how many games have troops / people / bad guys wearing masks? Or when you run up to someone they look just like all the others? Well that’s because face art and animation is very hardware- and software-intensive. DX10 support for GPU blend shapes allows major changes in facial animation and detail. In addition it’s now possible using state-based instancing (among other techniques) to have lots of people all with different looks and with facial animation. So for example your character could run into a nightclub or a village and have to find a specific person before it’s too late. That creates a tense new gaming challenge.