I don't think that's true .. My brother is in Oil field & according to him such rumors aren't true ..
Regarding salary ..I already explained in my previous comment, why it's different nationality wise ..

Its due to difference in standards & cost of living ..

Example - 1 Pkt of Marlboro costs 6.5 Pounds in UK, that's 35 QR ..Here it's for 10 QR , 3.5X the price ..
W.r.t cost of living ..I personally find qatar a lot cheaper except for Housing, I agree Housing is bit expensive ..But you can get them cheaper in places like Al Khor ..

Rest everything is much cheaper than the west ..