It is the "magic wand" syndrome, and the magic-wand is money. People in the West often turn to dumping money onto a problem as the first resort to solving it. In reality there is no real functional difference between a road and mountain-bike except for the tires each has to suit the road surface. I did a 42-mile road-race on my Marin Bear-Valley 25 years ago after pumping the knobby tires up to 80psi, and the only part of the race I was dropped on was long fast downhills where I ran out of gear, which a simply cassette switch would have solved. The sanctioning body banned riding MTBs in the race the next year. If you set up both your MTB and road bike to give the same body position, and run close to the same pressure in the tires, there will be almost no difference in their speed on pavement, the road bike will just be more comfortable for longer. I still have my Marin and it is not set up much different than my road bike, and it works great on dirt-trails because the low bar i great while climbing steep hills, and downhill I just drop off the back of the seat and put my butt on the rear tire.
