DAZ has made DOF a very quick and easy thing to do in Studio.

It is also a good way to hide those other things you mentioned; mismatched backdrop lighting and untweaked material shaders.

In portrait shots, The focus is sharpest on the eyeball and the area of focus is kept tight. In this shot the area is so confined that the tip of the nose and the other eye is out of focus. In practice that would take an expensive lens to do.

The sin being hidden here is LaFemme, LOL.

regards
prixat