Well, Australia Day isn't a made-up holiday -it's always been the 'National Day' (think 4th July). But it's just that the Meat + Livestock Board spotted a gap in the 'traditions' market and filled that gap in with some shrewd marketing.
Really? I've never really associated Australia Day with eating meat, but if we were going to organise something on that day a barbecue would be quite likely. But that's probably true of any day where we'd be organising a family gathering. It's certainly not like Christmas where you have to pre-order a turkey.
I do find it ironic though how barbecues are considered to be an Australian tradition. But then the most well known brand for barbecues, Weber is American.
