ASUS and ASrock are essentially the same company. (They are sister companies, ASUS is not the parent). Asrock does some some good stuff. I've had some great mainboards. They do two kinds: cheaper than competitor, and also "out of the box designs": like my s775 with AGP.
Why does the parent of ASUS/Asrock run two different brands? There isnt a simple answer to that. It is a combination of internal competition (good thing), running different product offerings for different markets (and avoiding grey market imports), and organisational/political reasons.
In my experience, I've actually had better reliability with my ASrocks than my ASUS's. And their warranty programme is just as good. So if you like the mb, go for it.
... some things in life just drive you bonkers. Especially the rubbish you see in forum posts