It is an imitated example of "special economic zone" in China.
When a country want to be rich, what they need is to remove restrictions.
But, it's too difficult to change laws all over the country.
Then, the easiest way is to designate small area as the special place where most of the legal restrictions are not applied.
This example in Saudi Arabia is so rare in conservative Islamic countries that I'm afraid that it would be the target of Islamic fundamentalismists.