ViaCad is switching to a "surface cover" they call it. I think the difference between the more expensive ones, is that ViaCad is not giving control over the degree of the generated cover. The control points get generated the UV, but are very sparse where they need to "Warp". It seems ViaCads follow an "IsoCurve"type of pattern where the others create a nice, full grid and drape as necessary. The ones that trim at the boundry need to extend and twist way out in space to generate the surface, but the sparse points become wrinkles on the nurbs surface.

Maybe Blowlamp can point this to Tim to look at. Control over the UV degree may get a better NURBS out of ViaCad.