Nobody seems to get this, but: Representing a polygon mesh with nurbs can increase (not decrease) the polygon count only. It cannot increase the detail!
Agreed, my point though was that a raytracer doesn't need to convert them to polygons therefore you can represent the same or more detail with the same amount of control points.An example would be if you had a single quad (2 triangles) it would simply be a flat surface, however, as a nurb surface it could have bends and twists in it.
To represent this in triangles you'd need to have many many quads. the more quads the better the representation.
A bit like a texture, the higher res the texture the closer you can get to it without it pixelating.
So if you have a mathematical curve, you will never lose detail no matter how close you were.
though with much less work for the computer rasterization can produce nearly identical results
This really is only less work because there is a secondary computer doing a lot of the work for you (the GPU) at the moment there isn't a raytrace card. Although looking at the link above it appears there may be such a thing, and from their claims of "there was a scene of a Boeing with 350 million polygons rendered in realtime" sounds pretty cool, although without seeing any evidence or indeed what they class as 'realtime' it's hard to say.