Hmm, I'm not sure about that. There are quite a few players in Australia as well - 2 majors (Qantas, Virgin) and a bunch of minors and LCCs (Jetstar, Tiger, etc.). Not all that different from the US with the three majors (post-merger), considering the US population is 15x greater.
And Sydney-Melbourne is the world's 3rd busiest route in terms of aircraft movements, and 5th busiest route in terms of number of passengers.* On both metrics it surpasses ~any~ single route in the US. So Aussies do know the value of frequency. And airport congestion in Australia is surely less than in the US (IAD, ORD, SFO etc are clusterf***s as soon as there's any kind of weather or other disruption).
I just think that the flying public in Australia simply wouldn't stand for some of the penny pinching moves that carriers do in the US - there'd be a revolt. The majors all run similar routes at similar frequencies and so they really do compete more on the passenger experience than the do in the US.
Don't get me wrong, I get the need for the RJs between mid-sized cities, of which the US has many and Australia not so much (Australian cities are oddly distributed in terms of size - they're either massive metros or tiny towns, not much in the 100k-500k range other than Canberra and a couple of others). It just seems weird to me that 70% of flights between say, Chicago and Toronto (two of the very biggest cities in North America) are on RJs.