i would suggest you do some research on the companies that you want to work for and send your CV direct to them.
. EVEN IF THEY DON'T HAVE AN AVAILABLE VACANCY!..... you'll never know!
from what i can see, most of these sites probably receive thousands of registrations and applications a day and they don't have a sophisticated system to actually sort the mess out. you are probably registered user number 2,033,012.....
. And unless your skills are really special (i.e. pole dancing, splits...that sorta stuff), I doubt you'll get noticed.
and as for employer requirements, then I guess they have certain requirements, i.e. their customers are mostly indians, so they would prefer an indian to serve indian customers....the language and color thingy...and if they are into beauty product sales, then they would require a young female to do a good job by potraying her own beauty...etc, etc....
and when they specify arabs only, perhaps they require a person who is a native arabic speaker or understand the arab culture really well?
so whats so discriminative about that? its all part and parcel of business. they are trying to filter out the barage of CVs sent to them by stating their requirements out loud...its fair to both employers and employees.
And for someone who has been studying HR Management, i don't think I'm qualified enough to give you a 101 on HR recruiting.....