Yep, he's right. Since nurbs are made from curves, they tend to be smoother. Most modelers use nurbs for organic-looking objects. Polygons, on the other hand are made up of faces. You can manipulate the vertices with extrememly accurate presicion, which makes it easy to design non-organic objects. The drawback to polygons is that you must have an unholy number of faces to achieve the smoothness nurbs would offer. As far as sub-divs go, all I know about them is that it is easy to model a vararity of objects without some of the restrictions you would normally get with poly's or nurbs. Sub's are a cross between poly's and nurbs, although as qu2k said, they are slightly more like polys.

Also, when you create polygonal primitive objects, they are always connected. It is one whole object. With a nurbs cube, however, the faces can be moved away from the object without any geometrical changes in the other faces and a nurbs cylinder has no top or bottom faces unlike a poly cylinder.