On using cantilever brakes over disk brakes in Valkenburg from Katie Compton's Facebook page, posted just yesterday:

"Katie raced her cantilever bike. It's lighter which on this course helps a lot and she has a better feel for braking traction with canti's over disc."

[Sven Nys stated the same last year, that his bike with canti brakes is lighter -- these are folks that have a choice in components and ride new bikes.]