If I read you right, you are saying some audiophiles can tell the difference between a very expensive Ethernet cable and a normal-priced cable that meets the spec (with enough over-engineering so it continues to meet the spec after installation and in the face of environmental changes and normal levels of RF-noise)? I'm just not seeing how this is possible. Well, MAYBE if the cable is running through a very hostile environment well outside of what a "normal" Ethernet cable is designed to handle. But if that's you, then you've got bigger issues to worry about.
Oh, the audiophiles do have a point about cheap Ethernet cable: Every now and then, you will find cable that actually does not meet the spec. You will also occasionally find cable that barely meets the spec but as soon as you bend it a few time and the wire-strands start to break, it drop below spec. If you buy a reputable brand from a reputable vendor, you shouldn't have this problem. But in most markets you won't need to pay much if any premium to get a "known reputable" cable vs. "it tests okay out of the box but will it last over time" brand.