A large number of audiophiles, to include reviewers, claim to hear noticeable improvements when stock fuses are replaced with "audiophile quality" fuses such as Synergistic Research Quantum Red and Audio Horizon fuses. Assuming the SR and AH fuses are not snake oil, then IMHO designers are remiss for not using them.
11-05-14: Rockyboy
Are the fuses safety Listed by any recognized independent testing laboratory, such as UL? If not an equipment manufacture could put his company at great risk in the event the fuse did not blow and the equipment was responsible for a home fire.
Assuming the SR and AH fuses are not snake oil, then IMHO designers are remiss for not using them.
Same for aftermarket power cords how many aftermarket cords are safety tested by an independent Listed testing laboratory? The only one that come to mind is Shunyata Research power cords. They are UL listed.
As for fuses making a difference I personally don't know if they make a difference. I do sit up and listen when I read a post by Atmasphere they can make a difference. I would be willing to bet the fuses Atmasphere uses in his amps are Listed fuses though.
As for aftermarket power cords from my personal listening experience they do make a difference, YMMV.