This is totally ridiculous, but a lot of time there is a grain of truth behind some of these myths, that is just diluted by retelling from non technical people. I had a serious musician once tell me that if I rip a recording from a DAT tape to my disk it won't sound as good. It sounded about as stupid as this this claim, but the basis of it was conversion between 48khz and 44.1khz sample rates.

I also remember a friend of mine learning graphic design many years ago, who told me that their teacher told the class Photoshop on Mac produces higher quality images than on a PC. I don't remember what the basis of that was.