Hi Steve, that could potentially work for curves, but for surfaces the structure of a NURBS model can be very different than how polygon mesh geometry is structured and that generally means that there isn't really a direct way to use the exact same tools that you would use with polygon meshes.
A NURBS model can be built out of "trimmed surfaces" - this is where there is an underlying surface that then has trim curves on it which mark different areas of the surface as inactive or holes. This means that there may not really be any correspondence between the surface control points that you would yank around and a particular edge - it's very different than in a polygon modeler since in a polygon modeler an edge or point that you see in the model can be pulled around and it pulls the surface too because surfaces in the poly modeler (polygon faces) are fundamentally defined as going through those points and through those edges.
Here's a bit more description of a "trimmed surface" - here I have a surface:
Now if I turn on control points for that surface, you can see that there is an underlying surface that is just 1 rectangular surface with 4 corner control points in it:
It's those 4 control points that actually define the overall shape of the surface, all the edges that you see are all trim curves that are defining which regions of the surface are inactive.
But the trim curves are just markers - they do not themselves define the shape of the surface, that comes only from the surface control points.
So that means that it does not really make sense for example to try and grab this edge curve here and try to move it around (like pull it up or down in Z for example):
The thing that can be freely pushed around is the 4 outer surface control points, not that marker trim curve that is just living on the surface.
So just in general this kind of structure with trim curves just does not work the same way as a polygon mesh structure as far as squishing individual points of things around.
There is some more description of how trim edges and "underlying surfaces" work here:
http://moi3d.com/faq#Q:_Why_does_show_points_work_for_some_objects_but_not_others.3F
So you may ask - why use this structure at all if it doesn't allow for doing the same things as a polygon mesh?
Well, the answer is that this very same structure is the reason why Boolean operations works so much better with NURBS than with polygons - in a NURBS model when you do a Boolean the surfaces of the models actually remain exactly the same and only new trim curves are calculated to mark different regions of them as being inactive. This fundamentally helps keep things a lot more under control because your model stays in large logical sheets - when doing a Boolean operation in a polygon modeler the poly modeling program has to fragment things into a zillion little tiny sub surface faces because it doesn't have this way to have just a zone on an existing piece to be marked as being a hole...
This difference in structure is basically why there is a much different base toolset in a NURBS modeler versus a polygon modeler. But that difference is kind of what makes NURBS useful as a companion to a poly modeler, because it has a much different set of both strengths and weaknesses...
- Michael
