Some jobs require not just 500 multi PIC, but 500 multi PIC under the IFR (Cobham 717, Air North and Rex comes to mind).
It must be a uniquely Australian requirement because I don't see this requirement for multi-jobs overseas. In Indonesia, FOs get into airlines with just a single engine instrument rating and their first multi-engine endorsement is on a B737NG or A320. Although all that is changing now at the airlines' request with flight schools now starting to implent ME-IR courses.