Woo-yah! :-)
Thanks Michael! It's really nice to discover new things about MoI. That'll come in handy.

Southpaw...

I think Michael will have a more concise analogy of the differences in the technology.

But, from my knowledge, the differences between the types of modeling technologies are:

D-SUBS: Based on polygons, are "cages" defined by points that are subdivided until a smooth shape is produced.
You can add endless complexity to the cages at the expense of adding an exponential number of polygons.
Editing can be kept fast by working in "low subdivision" modes where all you care about are manipulating the cage control points.
D-SUBS allow for complex organic creation with ease of editing. But if you want smooth polygon surfaces, you'll have to up the subdivisions.

VOXELS: Based on arranging points that are filled in with "bubbles" or surface thickness. This is how Z-Brush works.
With these modelers you can create freakishly complex organic models - even down to goose bumps. Polygon meshes can be interpolated later for use in layout and rendering apps.
VOXELS allow you to create complex, life-like models, but not the type of models needed for manufacturing where tolerances are high.

NURBS: Which MoI is based on, uses spline based math to build liquid smooth curved surfaces from relatively few control points.
The trade off with NURBS surfaces is that you can create a nearly limitless number of polygons that conform to the desired surface with a high degree of accuracy, but you lose the ability to model high detail, convolutions and bumps as you can with D-SUBS.
So, MoI's simplicity and ease of use is based on that premise.
NURBS are geared towards manufacturing and product creation, where mechanical accuracy are required.