Like a few others, I thought this thread would be about "leff-tennant" vs "loo-tennant" etc. Instead, it's the old "our English is better than your English" thing. Everyone knows it is we Aussies who speak the best English in the world.
Seriously though, the reason English has been around for so long and is spoken by so many people as a first or second language is because it is so adaptable. For approx the last thousand years people have been saying "the language is going downhill because of the vikings/Danes/Normans/Americans and we have to stop it". To date the success rate of such plans has been zero. It's just how the language is.
English doesn't belong to the SE corner of England. It belongs to everyone who speaks it, whether they are in London, Belfast, New York, Delhi, Cape Town, Sydney, Wellington, Cairo, Tel Aviv or Rio de Janero.