Bustedknuckle said:
Vast majority of aluminum rims hold the tire fine, don't heat to the point of blowing off tires and die when they get bent or dented, rather than wearing out a sidewall.
PLUS the advantage to MTB are things that are seldom seen on a road bike, a road bike, not cross or tourer...wet, muddy, crappy conditions and high chance of wacking a wheel.
Disc brakes, wheels, frames, hubs will never be as cheap as rim brakes. I've seen rim brakes for $15, new, Tektro and they work OK.
Lets look at the equipment racers are using and not how cheap a part can be made. No one is racing on 15 dollar brakes nor are many top racers using aluminum rims. So we aspire to greater access to exotic materials at lower price points. A lot of modestly priced road bikes are less than 20 pounds but not cheap bikes yet.
In the sport of cycling the rules shape the material to a large degree. Frame shapes, weight and in this case brakes. There has been no demand for road bikes with disk brakes but at some point racers will chose based on performance and weight will be a moot argument.
As the parameters change so will the result. As it stands today disks are a weight penalty. They are currently not much of an advantage for most courses but are much less a penalty today than a year ago and 2 years ago it was against the rules.
In another year the equation will have many new variables.
One other point about price.
Take the most technically advanced bike from 1986 and compare it to a $2500 bike of today. I think the bike of today will be as light or lighter, will be stiffer, will have 4 more cogs, and enjoy a lot of things that were not available in 1986 at the dawn of clippless pedals and index shifting.
Actually this argument is inane and almost every time somebody demands a technology is a waste of effort or it won't take hold or it is too expensive that they get proven wrong or miss the mark. Eventually all technology gets cheaper as it gets more expensive and exotic.
You can still buy $5000.00 computers but almost any $500 computer built today outperforms a 5 year old computer that was $5000 new