On off road bicycles, disc brakes are superior for several reasons including the disc is not dragging through the mud which gives the brake pads a clean surface. Also if they are hydraulic, then it is a closed system so water and dirt don't get on the cable. Stopping power is greater and the modulation is better (doesn't suddenly grab at some point). Those points are true but all less important on a road bike. However many high end bikes have carbon fiber wheels and disc brakes prevent the carbon wheel from over heating. Also the special carbon pads are annoyingly noisy compared to rubber pads and an aluminum rim.

Personally I still have rim brakes on all my road bikes, disc brakes on my mountain bikes. Rim brakes have served me well and no reason to change just for that. However if I do buy a new road bike, it will have disc brakes simply because that is what everyone is producing.

Note, hydraulic disc brakes can fail as well on downhills. On a long (as in 2500 foot) descent in Colorado, a guy I was riding with had his brakes heat up so much on a mountain bike that the mineral oil boiled and he lost his read brake. We had to wait for it to cool down and then it was fine.

Dan