OK, so here is DX9 with 2X AA enabled....
And here is DX10 with 8xQ AA enabled...
I know these pictures are not that great, they really dont do what I'm seeing in real time any justice. But, notice the rotor blade in the DX9 photo has blurry jaggies...Well in real time those jaggies are moving, kind of sliding down the rotor blade. The DX10 pic looks a little better, but the picture does not show how much better it looks with movement. Yes, the AA in DX10 could be better, but I hope I'm making my point when I say that DX10 is not limited to 2xAA.
DX10 looks much better on my rig, and I'm happier with it.