As I understood it, one could use an 8-speed cassette with a Mavic Ksyrium wheel. That appears to be true - the 8-speed cassette I tried does fit on the freehub. However, I was also under the impression that the spacer that comes with the wheel is only for the 10-speed cassette. The instructions seem to imply that the spacer is for 8/9-speeds. I thought it was the other way around.
Look 585 Ultra, Pinarello Dogma, Pegoretti Duende, Orbea, Cannondale Capo
According to the drawings in the instructions, the spacer is for 10 speed, according to the text, it is for 8/9 speed. I believe the way this is written is that the drawing are the primary source of information and the text provides the exceptions.