The problem is only using 3D quadric surfaces for all the pieces that go into a model really limits the kind of shapes that you can construct.

You need to be able to build surfaces from curves in order to get a lot of things like text for example...

Groboto has the "better booleans than polygons" ingredient from NURBS modeling but the other big thing that tends to make NURBS modeling work particularly well as a contrast to poly modeling is being able to make a lot of the model formed from 2D curves.

- Michael