TATY - You're right, it was to do with people moving en masse to settle in other countries. Following website is good for details about different accents in Australia.
www.fut.es/~apym/students/Australian
I didn't realise that it is different there to England where we have lots of regional accents. If you came to Yorkshire to learn English you might end up speaking English with a Yorkshire accent if your teacher pronounced words with flat vowels. People in the UK tend to mimic accents from different regions. Some accents are more popular - easier to listen to - than others. I have very little accent because I moved around a lot - plus my mother made me have elecution lessons in an attempt to make me posh - it failed.