I'm pretty sure black roses have been used to symbolise all kinds of things which don't seem to be related. There's the Victorian death rose, but then there's its positive association with political anarchism and also devotion. It features a lot in fiction symbolising a wide variety of things.
I think it's as simple as it being popular because its really cheesy. It's a bit like tattooing a dragon, a Celtic cross, Norse rune or a skull. It just looks "cool" if that's how your tastes go. It gets to symbolise what ever you want it to.
It could also have something to do with this.
http://en.wikipedia.org/wiki/Black_R...rganization%29