plastic shrinkage cracking should be minimal in a 25mpa slab, especially in Melbourne. You are correct that it is not unusual to include a top layer of steel, but that is typical in suspended applications. Top steel is generally designed as per AS3600 where required in tensile zones that exist due to max moments in the top fibres near walls, columns, piles etc. It is also used sometimes to assist with tying stirrups for shear reinforcement and as you say control cracking due to early age, plastic cracks etc.
Sorry for getting technical, i am a civil engineer with a sub major in rehabilitation of concrete structures. I kind of get excited by concrete
