Quite the flair for the dramatic.
Have you got a real technical reason for the tirade?
What do you think the current carrying capability of a wire is?
Better yet is it rated for the wire or the insulation or both?
Wiring is rated for both the wire AND the insulation type. Wire has an ohms/foot rating. Current can create heat within the wire. One can actually calculate the watts consumed/dissipated in a given insulated wire example, if you now its specifications. The insulation must be rated to withstand the temperature created by the current carried within the wire. This is balanced by the environment the wire is present within. Ambient temperature and flow around an insulated wire can effect wire and insulation operating temperatures. There are many insulation types and temperature ratings, and well as wire metal alloys and purities.
74750k4's point about the bean counter's desire to minimize costs, is a valid one, and one reason that engineer's are employed. For example, copper cost money, minimizing copper consumption leads to cost savings. If a 22 gauge wire can survive in the same placement as a 14 gauge wire, the difference in costs, say $.50 per example, when making a million copies can pay for both the engineer's and bean counter's salaries, and increase the sales profits/volume due to lower sales pricing of the product.
I maintain that in the 70's era, the electrical systems were slightly overbuilt regarding wires, and had actual capabilities in excess of demand. Copper wasn't THAT expensive back then. When the electrical system was created, the fuse was selected after noting the expected circuit loads, which was about 10 amps. Common fuse selection criteria of the day, said to make normal current loads about 2/3 of rating, resulting in a 15 Amp fuse. This was NOT a result of noting what the wires could actually handle at maximum current for all branches. But rather, a choice based on observation of what normal loads were. As a safety device it only had to account for what was abnormal for the circuit, and both 15 and 25 amp fall into the same category for this equipment arrangement.
The fuse holder type and it's current capabilities are a different engineering matter. I wouldn't want to use more than a 20 amp fuse in the stock fuse holder used on a SOHC4 that stipulated a 15 Amp fuse. Even then, I'd make sure the the fuse holder was in operational peak condition. I suspect the SOHC4 fuse holder was selected based on prior specification of the fuse chosen to be used. I believe that the fuse holder would have been of different design and materials should a 25A fuse been the norm for use. Indeed, the 30 A fuse of the CB650 uses quite a different style than the other SOHC4s.
