Why do salaries for the same role varies widely between western and local candidates?

I totally agree with what has been said from the previous comments. But let me just add a point to that. Aside from the fact that they put more weight to the value of education and experience to Western educated candidates they also put into consideration the cost of living in Western countries. It is known of course that most of them are away from their families, and they must send money to support their families. So if you're going to compare the value of AED to EURO or GBP, theirs is much higher and their salary here must suffice their families' financial needs.

There has been a practice in the Middle East to discriminate based on nationality and this is largely why salaries will vary depending on the nationality.  This has changed over the years and is not as pronounced as it used to be.  Traditionally, the standard of education in the West was deemed to be at a higher level and the quality of the experience that candidates brought with them was also highly valued and this has also led to variances.  These variances are being eroded with employers veering more towards paying the market rates for jobs.  Plus, in the boom times people could demand the salary they wanted - this too  has changed.... 

There has been a practice in the Middle East to discriminate based on nationality and this is largely why salaries will vary depending on the nationality.  This has changed over the years and is not as pronounced as it used to be.

because we are sill use our Local Vitamins in selecting any candidate against to select him upon his professional career :) have a nice day.