But, for all the disc fanboys out their, may I just remind you that some motocyles are switching to rim mounted brakes because they offer better braking/lighter weight/better handling.
The rim mounted motorcycle brakes have very little use. Currently, they only have applications for Buell Motorcycles (the sportbike division of Harley Davidson). Other than that, their only appearances have been on concept motorcycles, most notably, Honda.
But if memory serves, they were originally developed by Braketech, an aftermarket supplier (targeting, btw, Buell applications!)
History lesson aside, they actually have some significant drawbacks. These are greater gyroscopic moment than smaller twin discs, and lending to fork binding (increasing fork stiction since it's bending only one fork under braking).
So why does it work on the Buell XB9S? 1) It's got really short and steep chassis geometry, even by racebike standards. The big disc returns some of the lost stability. 2) It's not a racebike, so they're not as concerned with a little extra fork stiction.
I'm not saying that these are major problems for a streetbike; it's more a question of fashion... but you won't see them on a racebike.