I suppose I've been used to Nick Fury as a white guy, and wasn't aware that he's now black in the Ultimates. After I saw the screenshots of Hasselhoff as Nick Fury, I'd rather see SLJ in the role. I think bottomline, it's really about finding someone who fits the role. There aren't too many white guys of late that can fit into the Nick Fury mold. They're either too pretty boy looking, and not enough toughness. A parallel to this would be finding anyone else who would've nailed Wolverine outside of Hugh Jackman (preference to a Caucasian actor who is short, squat and bad attitude).
For Fury, I can't think of anyone white who can fit that role.
Thank goodness Robert Downey Jr was cast as Ironman -- there's a good chance he can sell the role, even if the plot stinks.
A bit OT, but did anyone feel that Eric Bana filled Hulk's shoes (rather Bruce Banner) pretty well? Somehow I didn't feel he sold the idea of conflict within him too well. With Norton in the upcoming remake, I'm still on the sidelines on this one.