Good hydraulic discs modulate really, really well. Better than dual-pivots, IMO.

I was told that one reason why you dont see too many disc brakes on road bikes is that they put a lot more torque/stress on the hubs and the fork - sounds plausible, although I dont know whether is really is true or not.

Also, I would assume that the chainstays and fork need to be wider in order to accommodate the rotor, which would be less aero.

V.