These urban counties are all going Dem in a big way as Republicans flee ever further out into the sticks and minorities multiply. I don't think you can read much into a poll of one county.
I think its wrong to think of Duval as an urban county. Its big enough to encompass both Jacksonville's suburbs and some of the exurbs as well. And most of the city outside of the core is virulently republican. The county voted for Bush both times at about 57-41 and its very bad news for Romney if he can't do better there. In the end I expect it'll go for him 55-45 or so.
