I would disagree somewhat with the latter point. Casual cyclists who ride a few miles at a time may rev low, but many riders who go out for fun rides of 5 miles or more tend to pedal at 80 or above. Those who actually do "go long distances at high speeds with as little effort as possible" will predictably be at 90-100 rpm. Racers will be in the 100 - 110 range most often.

As long as we've gotten on this tangent I may as well talk about some of the why for high revs.

Mechanics/physics plays a part. Pedaling forces are off-center to the plane of the bike's direction. That means that there is a both a levered force to each side and torsional movement. If one pushes harder at low revs more of one's effort goes into rhythmically stressing parts, which is dissipated as heat. In addition, due to the off-center pedaling forces, the bike will to some degree lean to one side and then the other and actually deviate from a straight line. Both effects waste energy.

Physiology plays an additional part. When you pedal with higher force and lower rev's the muscles more easily build up lactic acid due to higher stress and less efficient transport of oxygen in and waste out, so they become less efficient. Yet it does not increase strength as in weight training. In weight training you are pushing directly against the ground or against a fixed object such as the back and seat of a machine, whereas the bike, as noted above, absorbs or transferring your effort. It is mostly with high speed that one increases fitness at high gears and (slightly) lower revs, with the sole exception of out-of-the saddle climbing.

When spinning the blood flows more efficiently, and because one can go faster it's easier to get the heart into better shape due to the aerobic effect. Oddly enough, once one has done so for a bit the muscles and heart and muscles become more efficient, and the cyclist who spins expends fewer calories than a masher to go the same speed.