The detail mentioned was first used by the Vales in Sheffield, Yorks. in a series of energy-efficient buildings c. 1986 onwards. It was designed to avoid
(1) air leakage and
(2) risk of partial collapse of ground floors into abandoned cellars on brownfield sites (apparently a serious local problem!)
Prof. Bob Lowe, among others, has tested a lot of buildings with a slab resting on the ground. The junction of slab and external wall usually shows considerable air leakage, even though in theory the DPM under the slab could act as an air barrier. This is due to the small gap at the base of the plaster esp. as the slab settles.
If the DPM was capable of maintaining its integrity, and acting as an air barrier, there's no reason why a slab on ground couldn't be used. In practice, though, surely the edge of such a membrane is likely to be damaged as the slab settles or damaged as the slab is poured.