I am almost positive the black cat has more significance that what we have seen thus far. Remember Arhu (sp?) in the first game appeared as a cat. And if you pet pal the cat gives you a couple clues that there is more than meets the eye going on, most likely amnesia of some kind.
My guess is that because this is EA and only ACT 1 - which does not have all the content implemented by the way - that perhaps there is a plot point revolving around the black cat that they did not want to reveal just yet. But either way we only have 8 more weeks until we will know for sure.
