I'd say that it doesn't matter whether they're matching or not. =] It depends on the couple involved as well as the two individuals themselves.
It doesn't really matter to me. I always thought it would be cute to have two different rings than when you put your hands together they made a design or serving.
I don't think it matters if they match. Might be cute if they do, but they certainly do not have to. Whatever works for the couple in question.