video / texture mapping : nurbs pixelating more than mesh ?

Following the Jitter Recipe book n°18 : Manipulator, and comparing it with things about keystone and mapping found here and there.

... it seems that jit.gl.mesh gives a better result than nurbs when manipulating texture displacement ... Why does jit.gl.nurbs pixelate the result ?
or is it just a feeling ?
Also, i don't succeed in making an equivalent grid to manipulate a mesh in the same way as the jit.gl.nurbs ... I tried to start from the keystone patch from hc gilje here : https://cycling74.com/forums/corner-pin-adjustement-of-planequad-with-videotexture

I understand mesh requires 2 more planes, but i don't get it to work ...