790GX has no onboard graphics. Or at least the board you have linked doesn't. The second 790GX link has onboard.

No onboard here (first link) GIGABYTE GA-E7AUM-DS2H LGA 775 NVIDIA GeForce 9400 HDMI Micro ATX. The 790GX you linked has onboard video.
 


Onboard graphics solutions are associated with the chipset. My best guess as to which chipsets offer the 'best' solution. Intel G45, AMD 790GX and ATI 690 are the top of the respective line onboard graphics solutions currently.