Well actually this is only true on a hard surface, like ice. On snow the middle of the board will sink a little deeper and thus create a multirate radius... The only thing is, when I calculate this radius it actually should be longer radius in the nose and a thighter in the middle! And then the same from the middle and to the tail( If the board is ridden with a central weight distribution). This is particulary true if the board is leaned over more than 45 degrees. And in those turns the clothoid or elliptic, which both has a longer radius in the middle (what is the difference??) will work against the board and the board will not have as good egdegrip as a single or slight progressive radius. This is not just math. It is exactly what I experiece with for example the boards from Virus.
But I must admit that a clothiod or elliptical sidecut is fun and reactive in normal carving conditions. It is only when you tilt the board more than 45 degrees that you actually can feel a slight decrease in edgegrip. I do ride rather agressivly but whit a very centralized stance so another person with an different riding style, might disagree with this.;)
I know some of you do have other opinions and I look forward to read them.