First of all, I believe the survey figures are not correct. I agree that people from countries like Pakistan, India etc accept jobs on less salary. There are usually two reasons for that, first; the cost of living in their country of region is not as high as western countries although at times they enjoy better life style back home as compared to an average person from western world and interestingly at much lower cost.
The second reason why at times they accept lower salary is that sometimes they do not have fair idea of cost of living being so high for a place like Qatar. Life style in Qatar is by no means comparable to the cost of living in Qatar. For example I am paying QR 8,000 for a pathetic 2 bedroom apartment which is same as six month rent of the similar apartment in KSA. How someone like me who was switching job from KSA to Qatar can imagine such high rental prices. Ofcourse I visited Qatar Living before switching job and try to get fair amount of idea for cost of living in Qatar but unfortunately cost of living is relevant thing. Something expensive for someone can be cheaper for another person. So I perceived the wrong cost of living in my mind and made the decision of switching job. There are no photographs available online for rental apartment so one cannot access it until he is here and see with his own eyes. One cannot trust the employer supplied cost of living figures. This is true for people from low cost of living background as compared to people from higher cost of living backgrounds. People from US & UK ask for more salaries because they based it on their cost of living back home which is somewhat comparable to Qatar. By the way I can rent a really nice two family house in Pakistan for the amount of rent I am paying for the place I am living in. I have been to New York, where I done my masters and I know I can get a house on bank loan in the amount I am paying for my place in Qatar. It is just like draining money in the sewer. My sister is in NY too and she has her own house (mortgage) in Hicksville and paying similar amount to the bank every month. I do not have any regrets as I am quite content with what I am earning (better than majority and more importantly good enough for me) and I was the one who accepted this offer although I was ignorant of the correct cost of living in Qatar. I am just trying to convey the message. It is just a thought which at times comes in my mind that I could have been negotiate better had I know the correct COL. Without having the same baseline of comparing salaries between nationalities such surveys are useless. I have seen people from Pak and India earning salaries similar to western expats. The point is that you should know your market value, cost of living of target country and salary range for similar positions. After that, it all comes down to salary negotiation where I would give more marks to western expats as they really know how to negotiate the salaries well.