Tangan & Wirgin, The fare is not cheaper than the flexsaver and is only cheaper than the full flex on the shorter flights such as SYD-MEL. I can buy a flexsaver tomorrow or in 6 months time on a 767/A330 cityflyer service for $80 less than the Premium Econ (SYD-MEL).
Also on the lower end fares QF is far more accommodating to move passengers to earlier flights (if space permits) on the day of travel free of charge, don't need a lounge then because i just get on the first available flight.
And to compare Premium Economy with Business class shows you have not travelled on either of them (especialy if you paid for PE and travelled on an Embraer).