There is one very important issue concerning the desire of most Chinese Schools, Universities, Colleges and Private Training Centers that seems to be missing in the arguments back and forth concerning these insitiutions requiring native vs non-native speakers/teachers. No less than 25% of all my classes, regardless of the course title, have had to do with "culture". The truth is that the Chinese learners of English want to know mostly about the culture of the USA and the UK. This holds true in Business classes as well as Language classes. I presently teach courses in Finance and the students want to know about this vis-a-vis the US, not the Philippines or Cameroon.
A non-native speaker cannot easily speak to these issues and in addition cannot easily talk about the culture of say the USA. It is unfortunate, but presently true, and until such time as the "cultures" of other countries become more of an interest to the Chinese learner of English, the schools in China will no doubt continue to want native speakers as their first choice.