The LAX-JFK and v.v. flight also is timed to connect with the LAX-MEL flight as well as the LAX-SYD flight. I remember years ago flying this route with only 100 PAX on board but earlier this year I did it on a Saturday night and was told the load was close to 300.
We may one day see a SYD-DFW non stop with any luck but I cannot see a SYD-JFK non stop happening unless the cost of fuel forces those with private jets back into F/ J on commercial carriers. With the demise of the US investment banks and private equity market I can actually see QF's premium cabin loads dropping significantly for the next 24 months anyway.