Or, and this is a remote possibility, they may not have exactly the same motherboard as you. Crazy, I know.
Onboard sound is like onboard LAN, onboard RAID, onboord graphics ect.
It's cheap, crappy and just...just useable.
Hell I can't even stand to listen to a 196Kbps MP3...I think people have never heard good sound.
I am serious here..."loudness wars" and lossy MP3's have gotten people used to subpar quality.