Gill,
ZBrush is for organic stuff first of all, but it has tools that allows you to create hard surfaces too. But result is far away from ideal. Quality of organic surfaces are even worse then from polygons.
It is good for games because in games you will see only low poly, so no need for superb quality, or it is good for intermediate quality render of hard surfaces.
If for example you create some close render of this model you will see how imperfect are surfaces, I can see all that artifacts even from this render.
So if you want superb result use Cad.
If MoI had continuity(tangent) options in tools you could made this model without problems in MoI.