FBinNY 

I'm about as far from being a fan of disc on road bikes, but purely on a basis of rotational weight, they may turn out to have an advantage.

Yes the disc adds weight, but as pointed out it's near the center. OTOH they allow the use of CF rims without brake tracks. That shaves a decent amount of weight where it matters most, so on balance a CF wheel with disc may have lower total inertia than one made for rim brakes.

But that may be their only advantage, along with better rain performance. The flip side is that they introduce new issues such as increased stress on fork blades, wheel mounting issues, and higher cost to own and operate (at equal quality levels).

It's long been my opinion that the push for disc on road is driven, not by technical superiority, nor consumer demand, but by an industry that, like a shark needs to keep moving to surviving. Makers need to sell ever more expensive bicycles, and convince those who already own bicycles to upgrade to the latest and greatest. In this way the bicycle has become like the computer and cell phone industries in trying to force a planned obsolescence on their customers.

This isn't to say that there's no place for disc on road or "pavement" bicycles, just that we should be honest and stop claiming that rim brakes which have served so well for a century have suddenly become barely adequate relic of the dark ages of bicycle tech.