I guess that the rational behind it is that native speakers will have the 'best' English. Of course, that is open to plenty of interpretation, but they will be more familiar with it as it is their first language.
**PLEASE NOTE** Before you start having a go at me about how racist I am, I am not saying that a native speaker makes a good teacher!!
A good teacher can be native or non native, the qualities vary from person to person. Okay?! Don't dump on me about the rules and the fairness of it all, talk to the Chinese authorities and customers. I know already!

As for the 'type' of English. Well, I have had Chinese come up to me (plenty of times)and ask "Should I learn English English or American English?" I reply that you should just "Learn English" If you speak US.E or E.E you will be understood no matter. *Trying* to put on an accent is just plain silly, though some students do pick up accents from teachers if they have them for a long time. Most Chinese students have a Chinese accent!

> What's this rule in Korea about hiring only 'native' teachers?
> Surely, such rules exist in other countires, too. I have been reading
> the posts here for some time now and am amazed at the negative
> perception many recruiters, teachers and students share about
> 'native' teachers. One went to the extent of comparing them with
> peasants in China, not that there is anything wrong with peasants.
> Yet, S. Korea in particular, and many schools in China, Vietnam,
> Japan and other countries 'insist' on hiring native teachers. Is it
> because looks sell? Is it because education has become merely a
> business, perhaps, little more than a scam? Is it because the
> language is less important than an accent?
> English is an international language, spoken and used in hundreds of
> countries across the globe. This widespread use of the language has
> served only to enrich English in many ways, making it more vibrant
> and beautiful.
> Unfortunately, these days, there are millions chasing fake accents
> and designer dreams. To me, it sounds pathetic when I come across a
> young Asian with a heart full of aspirations launch hesitantly into
> an English conversation with a North American accent and then trip
> over the simplest words, phrases and grammar. Surely, it's not the
> youths' fault. The crime was committed by another but the price is
> paid by the unwary.
> Please stop this exploitation of the young. They need to be taught
> and treated as students and not merely commodities, a market, a
> statistic.
> They need to learn to communicate and use the language effectively
> with people from all over the world. While an 'accent' may impress a
> few for a while, ultimately it will make the user look silly and
> shallow if there isn't much else to back it up. A ticket printed on
> gold paper will not make the voyage sweeter or safer or more pleasant
> - especially not, when the boat leaks.