Well I hear differences, but my hearing and system are quite good. Granted, some differences may be subtle, however others are quite obvious. For example, silver sounds very different than copper.
Just this weekend I've been comparing outlets, the Hubbell 8200/8300 and 5362. The only real difference is that the 8200/8300 has nickel plating whereas the 5362 does not. The presentation is different, with the 8200/8300 being more forward, brighter, and a bit of glare. I attribute the differences to the nickel plating.
I have a friend that is a cable denier. Whenever he comes to my house he pokes fun at the fat hose pipes that adorn my system. Last time he was over he commented that I had more bass then before, and what had I changed. When I told him it was only one IC and a PC, he just grinned.