I'm not quite sure of your point, Australia is a relatively small market with basically three high volume routes, US probably has in the order of 100+ (if not greater) routes with similar volumes, comparing SYD-MEL with America seems extremely simplistic at best.
And for me at least, making simplistic comparisons is the antithesis of intelligent behavior, which we seem to be expecting of the airlines. If we expect it of them, we should also apply similar expectation on ourselves and our own commentary.
The US doesn't have a single dom route with the volume of Australia busiest 2 routes. Even looking at the top 10 it's not that different. I agree that there are more potential city pairs in the US, but purely based on high volume route the US is not a leader.
[h=3]United States (September 2014 - August 2015)
[edit][/h]Busiest air routes by city pairs within the United States [SUP]
[12][/SUP][TABLE="class: wikitable sortable jquery-tablesorter"][TR][TD="class: headerSort, bgcolor: #EAECF0, align: center"]Rank[/TD][TD="class: headerSort, bgcolor: #EAECF0, align: center"]City 1[/TD][TD="class: headerSort, bgcolor: #EAECF0, align: center"]City 2[/TD][TD="class: headerSort, bgcolor: #EAECF0, align: center"]Passengers
(Sep 2014-Aug 2015)[/TD][/TR][TR][TD="align: center"]1[/TD][TD] Chicago, IL (Metro Area)[/TD][TD]New York City, NY (Metro Area)[/TD][TD]4,020,000[/TD][/TR][TR][TD="align: center"]2[/TD][TD]Los Angeles, CA (Metro Area)[/TD][TD] San Francisco, CA (Metro Area)[/TD][TD]3,660,000[/TD][/TR][TR][TD="align: center"]3[/TD][TD] Los Angeles, CA (Metro Area)[/TD][TD] New York City, NY (Metro Area)[/TD][TD]3,420,000[/TD][/TR][TR][TD="align: center"]4[/TD][TD] Chicago, IL (Metro Area)[/TD][TD] Los Angeles, CA (Metro Area)[/TD][TD]3,010,000[/TD][/TR][TR][TD="align: center"]5[/TD][TD] Miami, FL (Metro Area)[/TD][TD] New York City, NY (Metro Area)[/TD][TD]2,750,000[/TD][/TR][TR][TD="align: center"]6[/TD][TD] Atlanta, GA (Metro Area)[/TD][TD] Chicago, IL (Metro Area)[/TD][TD]2,720,000[/TD][/TR][TR][TD="align: center"]7[/TD][TD] Chicago, IL (Metro Area)[/TD][TD]Minneapolis, MN (Metro Area)[/TD][TD]2,720,000[/TD][/TR][TR][TD="align: center"]8[/TD][TD] Atlanta, GA (Metro Area)[/TD][TD] New York City, NY (Metro Area)[/TD][TD]2,600,000[/TD][/TR][TR][TD="align: center"]9[/TD][TD] Atlanta, GA (Metro Area)[/TD][TD]Orlando, FL (Metro Area)[/TD][TD]2,620,000[/TD][/TR][TR][TD="align: center"]10[/TD][TD] Chicago, IL (Metro Area)[/TD][TD] Washington, DC (Metro Area)[/TD][TD]2,620,000[/TD][/TR][/TABLE][h=3]Australia (2015)
[edit][/h]
See also: List of the busiest air routes in Australia by passenger traffic
Busiest domestic air routes in Australia[SUP]
[13][/SUP] (all passengers including connecting)
[TABLE="class: wikitable sortable jquery-tablesorter"][TR][TD="class: headerSort, bgcolor: #EAECF0, align: center"]Rank[/TD][TD="class: headerSort, bgcolor: #EAECF0, align: center"]Airport 1[/TD][TD="class: headerSort, bgcolor: #EAECF0, align: center"]Airport 2[/TD][TD="class: headerSort, bgcolor: #EAECF0, align: center"]Passengers (2015)[/TD][/TR][TR][TD="align: center"]1[/TD][TD] Melbourne[/TD][TD]Sydney[/TD][TD]8,613,400[/TD][/TR][TR][TD="align: center"]2[/TD][TD]Brisbane[/TD][TD] Sydney[/TD][TD]4,476,200[/TD][/TR][TR][TD="align: center"]3[/TD][TD]Brisbane[/TD][TD] Melbourne[/TD][TD]3,353,800[/TD][/TR][TR][TD="align: center"]4[/TD][TD]Gold Coast[/TD][TD]Sydney[/TD][TD]2,618,300[/TD][/TR][TR][TD="align: center"]5[/TD][TD] Adelaide[/TD][TD] Melbourne[/TD][TD]2,311,000[/TD][/TR][TR][TD="align: center"]6[/TD][TD]Melbourne[/TD][TD] Perth[/TD][TD]2,138,900[/TD][/TR][TR][TD="align: center"]7[/TD][TD]Adelaide[/TD][TD] Sydney[/TD][TD]1,831,500[/TD][/TR][TR][TD="align: center"]8[/TD][TD]Gold Coast[/TD][TD] Melbourne[/TD][TD]1,812,300[/TD][/TR][TR][TD="align: center"]9[/TD][TD]Perth[/TD][TD] Sydney[/TD][TD]1,760,900[/TD][/TR][TR][TD="align: center"]10[/TD][TD] Melbourne[/TD][TD] Hobart[/TD][TD]1,493,600[/TD][/TR][/TABLE]