re discs and pads; they vary.
On a bicycle, if you are happy with organic pads with a low metal content (BTW I find they are often nearly completely useless when properly wet) then the disc rotors can have a low wear rate. If you use sintered pads you get more consistent braking but higher wear rate. Other pads with an organic (or 'resin') base have various amounts of metal etc added and are variously abrasive/disc wearing.
Shimano appear to be using a rather abrasive pad compound as standard in their current road disc brakes; in combination with their ice-tech rotors the wear rate of the disc seems very high to me; often the discs themselves are at or beyond the allowable wear limits after just one or two sets of pads have been used. I think they have chosen a high friction coefficient so that the brakes feel good (despite relatively small rotor size) at the expense of life.
On normal (roadgoing) cars with disc brakes, for many years the pads could be 'filming' type, whereby in the dry the pad deposited a layer of material on the disc, and subsequently the disc barely wore at all. This worked well unless the brakes got wet or muddy, in which case the film would be disrupted and the brakes would (effectively) need bedding in again. Using such pads, a set of brake discs could outlast the rest of the vehicle, provided they didn't go rusty. In that era, all that was required for good safety on the road was that disc brakes worked as well or better than the brakes on most other vehicles, which at first wasn't that difficult, as there were still plenty of vehicles with rather poor brakes.
However as more vehicles were fitted with disc brakes and technologies such as ABS were introduced, some manufacturers started fitting more abrasive pad compounds. In simplistic terms these worked by keeping the disc face clean, at the expense of disc rotor life. This meant that the brake could be made to have better 'cold bite' and could be made to behave more consistently (important for ABS operation) regardless of brake temperature.
It also meant that the brakes were more resistant to contamination; with 'filming' pads fitted, a couple of greasy fingerprints on the disc could spell disaster. With abrasive pads, not so much. Typically the service interval for brake disc replacement went from 'as needed, maybe never' to ' about 30000 miles (or two sets of pads) if you are lucky' . For the last couple of decades or more pretty much every vehicle sold has been fitted with abrasive pads and brake discs that are expected to be changed several times through the vehicle life. You can still buy aftermarket pads which are kinder to the discs, but they also usually have noticeably poorer 'cold bite' and do not usually perform as well in cold braking tests.
In bicycle rim brakes the rubber compound can vary and so can the filler in the recipe. If you look at a brake block under a microscope you can sometimes see particles of (potentially abrasive) filler in the material. These brake blocks will always wear the rims; clues that you have this type of brake block include that the brake is noisy at all times (even in the dry with new brake blocks fitted) and that the brakes work fairly well in the wet, even if the brake blocks don't have good slots in them.
However by far the most likely cause of severe rim wear is that particles of rim material (much more likely when using rims with a machined braking surface) and/or dirt get embedded in the surface of the brake block and once this happens it becomes an accelerating process, with positive feedback if you like. Often you can hear the difference when using the brakes; I will stop, investigate and correct if I hear funny noises but many other riders seem completely oblivious to what is happening, until their rims wear out.
As others describe, provided the brake block compound is not too abrasive, they are free from debris, and used in clean conditions, aluminium rims can appear to be polished by the brake blocks, and can last well. However this is often accompanied by less good braking performance, especially in the wet. It is all swings and roundabouts; there is no such thing as a 'perfect brake', just ones that are, for any given task, better than others.