This is a common and well-known trend in imperial/colonial states: the metropole experiences the more drastic changes in pronunciation, while the outlying territories are much more conservative in their language progression.
An interesting result is that you can construct a fairly descriptive linguistic history of the United Kingdom just by looking at settlement patterns: Northern North America represents the English south ca. 1720, the American South represents Scots English ca. 1800, Australian English represents working-class accents ca. 1830, and South African English represents bourgeoisie accents ca. 1870.
*tries to say "guard" without pronouncing the "r"*
*sounds like a poor imitation of a British accent*
Very interesting article!
Murphy Brown: What is it with us? Why can't we take the easy road once in awhile?
Avery Brown: Because it's boring and dishonest and uncomfortable, like wearing a pair of shoes all day that pinch your feet.