Things to notice a) demo isn't very advanced at all b) you don't seem to have AA turned on
I got to say, I don't think its very impressive demo either, but I suspect it will look better on the RX4billion or whatever they called it
The reason it looks pretty poor is because PCA hardware doesn't use the features the demo is meant to exploit, therefore it just doesn't do them and why it plays without problems.
Think running a DX9 game on DX8 card if you know what I mean. It plays, but it doesn't look like it should