Originally Posted by
Koyote
This whole discussion misses the point, which is that people don't choose disc brakes for cost reasons. They choose them because the do steep descents in nasty conditions, because they need more tire clearance than can be had with rim brakes, and because (in the case of hydraulic disc brakes) they want massive stopping power with only light pressure from one or two fingers.
People choose discs on road bikes because they are transplanted mountain bikers, and erroneously believe that they need inappropriate ballast on their road bikes such as dropper posts, suspension, fat tires and discs. Your shop is definitely going to push discs hard because it ties customers to the shop for pad replacement, regular bleeding, rotor replacements, rotor straightening and rotor decontamination. At our shop we see way too much of this; in that it takes an hour to fix squealing discs because someone simply dabbed a rotor with greasy fingers. Plus discs add 20% on to the cost of a new bike.
If you are an all-season commuter riding a Surley with a rack and heavy panniers, then I admit you'll want discs. But discs on a go-fast road bike is an inconsistency; they add at least 2 pounds of weight, particularly on porky wheels. Plus they make the fork heavy and non-compliant, due to the bulking-up needed to deal with disc braking forces.