Why is the leader of China called president in English?

The title for Hu Jintao is 主席.  If one looks in dictionaries, the translation is 'chairman'.  Furthermore, the word for 'president' is 总统.  So why is it that Hu Jintao is always called 'president' by the media?  Is it China or another country that started this habit?  

I have my own theories, but I wonder if there is an established reason.