bernhard, you have to increase the tesselation... If you check 'show render tesselation' you will see the results in the viewport.
You cannot bypass this issue because of the way nurbs works (the mathematical method) and the way maya tesselates it to triangles for rendering (both in the viewports and in the software renderer).
Nurbs are infinitely smooth by definition, but Maya has to translate them to triangles for the displayhardware. Also small dense surfaces like fillets will always have an initial tesselation that is higher than large non-complex ones so you have to fiddle with the settings to get rid of cracks between them.