Disk brake rotors and pads have to be broken in as well which takes a minimum of one week, therefore a wheel swap would make the brakes near powerless mid-race, you would have to stick with the same pad and rotor for a grand tour for braking performance. It is true that rim brake pads have to be worn in as well but this process is much shorter (5 minutes?), the rims themselves are ready to use out of the box. The brakes should make a short fad in endurance races but ProTour is where they will not stay long. One more issue with disks are the differance in performance from brands, in rim brakes Sram, Shimano and Campagnolo are about the same in power disk brakes are very different in different brands riders running Shimano will have the advantage where riders on Hayes are will be way behind(here comes a flame war).