As I understand it, a cog system -- if its well designed -- should be fine. Whipple's statement is probably based on what they have factory tested and are willing to guarantee.
Now the more more you overdrive it, the more strain on the blower's internals, so if these come stock with a V belt or synchronous set up, people who try to up the boost probably switch to a cog system, and that may or may not cause overload issues separate from, but magnified by, a high efficiency cog set up.
On any blower, belt stretch, pulley warping, and damaged internals can happen as load increases, and the likelihood of that increases a lot as you increase the RPMs the blower turns at, so Whipple may just be sticking to the specs they have in print for a given blower, rather than panning a different set-up entirely.
Or am I on the wrong track here?
Bullitt, can you weigh in on this?