Whenever you search for a teaching job in China, first thing that you come across in most cases is that they are in search for professionals who are native English speakers, only professionals from a few countries such as the UK, US, Canada, Australia and NZ will be eligible. 

The idea behind hiring professionals from such countries could possibly be is that they have a better command over the language and the inclination of the Chinese to adopt their accent.

While I somewhat agree with the latter observation , I do not entirely agree that professionals from the select few countries have a better command as it is seen that Non native english speaking countries also have such people who have very good knowledge of the Language with near perfect dialect.

People like Vikram Seth, Arundhati Roy etc have won booker prizes in English which shows the fact that there are other choices available as well and while choosing a professional for a particular job it is important to judge by quality and not neccessarily the country!