Bicycle_man
I know for a fact of about 3 manufactures you can call and they will offer them in the equipment for a small upgrade cost, also that do recommend the better fuses as they do sound much better... And 2 of them are huge names in the business, but they simply don't try to push a product based on a small piece of metal as you say for exactly that point. They also believe they can improve the sonics having them in all spots on the board not just the primary fuse in that you see on the back of your unit.
Think about it for one second, do you not believe that the one small cheap fuse with a tin wire thats like the thickness of a hair on your head is not causing a small current drop directly feeding the primary on your transformer? So realistically a 20 gauge generic power cable on your DVD or receiver is good enough over the 14 gauge solid copper wire in your wall feeding it to that point?
The direction I cannot specifically explain, however it really depends on the leg the fuse is put on inside the equipment, seems that its normally on the HOT side, not the Neutral side which is tied to ground, so your 2 major AC lines which are hot and neutral back to your breaker box are in fact 2 different legs of an electrical system.
So I would assume the only reason somehow direction is effected is its just better in some equipment depending on how the neutral and hot are ultimately run into that component, some gear is actually wired out of "Phase" and some have Phase switches on remotes and on the faceplate sometimes just for this reason. Again who cares, if it works, yes I will say that a better fuse is in fact a better fuse, the cheap ones vibrate like crazy, have ridiculous hair like thin elements, and yes the isocleans and hifi tunings are quite a bit more substantial.
This is nothing new, for years CAR audio DC circuits have been using MONSTER sized fuses, big huge Gold plates inside the fuse element for complete current conductivity.. These fuses are of course much more amp rated than home audio gear, but take a look at the big battery fuses etc, and see that they replace the little plastic 50 cent standard car type fuses as well for huge amps and current drawing devices for competions in cars, realistically its just to get the best current without much voltage drop possible if the transformers demand it.