There are some potential issues with the combination of disc brakes, road bikes, small caliper, and excessive heat
this link that has caused a lot of discussion about over heating
http://www.bikerumor.com/2012/02/14/...ill-they-work/
interesting in this link manufacturers talk about disc and Shimano does not think for road bikes the rims can be made lighter..... not all mountain bike learnings will translate to road bikes
my synopsis: There is a potential oveheating leading to no brakes issue with smaller diameter rotors on road bikes in certain conditions. 'simple" answers like bigger rotors start to require design changes due to things like fork and stay clearance. Maybe road bikes will have to go to double front rotor. My prediction is that once heat dissipation issue is solved for smaller rotor sizes you will see a lot more disc brakes on road bikes
Interesting discussion of design issues in frambe builders
http://www.bikeforums.net/showthread...ions-and-traps
see
http://www.bikeforums.net/showthread...scs?highlight=