To that I say Skin Effect.
http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/skineffect/page1.html
Now I'm aware that this makes the most difference over long distances. However, the more sensitive the IEM or headphone the more likely that signal differences through cables can make a difference (if just a small one). Unless you are saying that every head-fier who can hear a difference is experiencing placebo, myself included.
And it is usually consistent, especially with 1+2 impressions regarding the Silver/gold cable.
If one reads that link, one is inclined to believe what they are talking about. But you need to actually understand it. His figure 3 for instance. 3 meters at 3mm cross section "standard" copper cables. I quote: "At 25kHz these values rise to 0·012dB and 0·028dB respectively". So.. What does this mean? There IS a difference. But, look at the figures. That volume change of rolled off highs is less than a fly farting across the room. Can you hear 0.0028dB? No. So a silver cable might measure better, but then the highs are rolled off maybe 0.0012dB. Is this better? Yes. But can you hear it? That volume change from the copper cable is akin to a fly farting at the other side of a football field.
If you go to college or read a book on the subject, you will quickly realize that "skin effect" is not applicable at all in the audio area based on its power, frequency and cable diameters.
Skin effect is applicable and important in multi-band gigahertz signal coax cable runs in lets say, antennas to software defined radios for the military or telecom guys. I know because I work at a company that builds said military gear. I am not an engineer, but the ones at my company laughed at me when I brought up the subject of audio and skin effect 5 years ago. One of them, also a audio nut of sorts, recapped his dac / amp combo with higher grade mil spec parts and a bigger, cleaner power supply. I asked him why, because if the parts in it are specced properly it won't make a sound difference? His answer: "Because I can."
Now, very sensitive iems driven at a very, very low volume might have a sound difference in the high frequencies. But at a level nobody listens to, like 5 dB. Blood rushing in your ear is louder. As soon as you turn it up just a slight bit, any difference has disappeared.
And yes, my personal claim, based on what has been measured and tested, is that all cables sound the same and anyone who hears a difference is enjoying a placebo effect. Don't get me started on amps and dacs now... But for me, the speakers / headphones differ in sound signatures the most. And the recording itself.
But I will say it again: I have tin ears. And it's your enjoyment after all. If you hear a difference, then you do! Enjoy it and be happy.
For me, the magic is in the music, not the gear. Imagine how much better DSOTM would sound if they had only used better cables!? Heck, it has tape hiss and even some spots where the tape warbles a bit, but it's undeniably one of the worlds greatest recordings / albums / music EVER. Especially for its time.