slo sho, you go right ahead doing what you want to do. It's a shame some people have to insult you and others like you for doing something that harms no one.
I have only recently taken to wearing an iPod on my long, slow, solitary runs* - but I don't listen to music, I listen to books. It enhances my enjoyment of the time I've chosen to spend alone, in surroundings of my choice, doing what I want to do.
Should I ever find myself in the odd position of having entered a marathon, I too will be waaaaaaay at the back, on my own, and if it's not against the rules, I shall take out my iPod and flippin' well listen to it.
*that would be all my runs, then.