No it doesn't. I misinterpreted your post if you were commenting on the reasons why people stipulate nationality, I thought you were commenting on nationalities being paid differently depending on their passports.
The reasons specific nationalities are sometimes requested for different jobs are varied and there is certainly truth in the fact that companies might advertise for a filipina office administrator because they are aware they can pay her a lot less than a western candidate, this is largely to do with how foreign qualifications are viewed and valued as opposed to race itself.
With housemaids I have always understood the request for a specific nationality to be a sort of code for the likely religion of the woman. Most people seem to prefer someone of the same religion working for them and vice versa. Also of course there are hundreds of thousands families employing maids from their own home countries so I guess they specify nationality for matters of culture and language.