The prices are set per region, the additional cost of say transporting the vehicle to Qatar, import taxes, customs duties, ect... The price on the web site is known as MSRP or Manufactures Suggested Retail Price. What we in the US do is use this as a gauge to start bargaining for the best possible price.

Just a note on unified pricing, I know you can get into a Mercedes cheaper in Germany than you can anywhere else in the world.