Maybe here a few reasons:

The P3-P5G33 supports ONLY low profile cards. And that may be more a problem to get a special card with low profile than a card that is not too long (i.e. Hauppauge WinTV-HVR4000)
And I'm very sure that the differences in speed between G965 and G33 are not that high, if there are differences....

The P2-M2A690G supports only PCI-e x1

But as always, if the system fits to your own demands than it is perfect. The Hetis 965 is perfect for me. I miss nothing.