Well, your ears are actually Petri Dishes of bacteria.
I suffer with chronic ear infections. I get them them 3 ~ 4 times a year. I have a semi-permanent drain tube in my right ear called a T-tube, and I need one in my left ear, but they won't do it in the doctors office any more, and when I had the one put in my right ear in the hospital, I stopped breathing on the table and almost died. So, I'm afraid to get the other one done.
Your ear canals can sweat and because of the elevated temperature, the ear wax and all the bacteria and all that can seep out and come in to contact with your headphones ... and that's probably what the smell is. I did notice on these headphones that my ear lobes touch the inner foam part. I've never had headphones do that before.
This is why I can never ever use ear buds. They are the most disgusting thing on the planet IMO.