In my opinion, communication is the best tool to improve one's language proficiency. In local, we are lacking of english speaking environment in our daily social life,thus we do not utilise the powerful tool of communication to brush up our proficiency. For those abroard, studying environment is a perfect place for them to interact with others, hence they are able to improve their speaking skill in English more efficiently as compared to us in local.
I have a good example of myself. Even though I am a chinese, I barely speak Mandarin before getting myself inevitably into a Mandarin speaking environment during my undergraduate study in local. Years of practising on speaking mandarin through my daily interaction with friends there has made me fluent in speaking mandarin.
"I'm convinced that ATTITUDE is the key to success/failure in almost any of life's endeavors. " ~Carolyn Warner