After I got home it occurred to me! That is a very simple, low level, and easy to make contrast. It's not important that he's black and that she's white. Just like it's not important that he's a smoker and she's a non-smoker. Nor is important that he's a man and she's a women. Those fundamental differences don't matter in a presidential candidate. Things like: race, religion, gender, sexual preference, hair color, etc don't matter either! What matters is that the person would make the right decisions should they make it to the White House.
The fact that Mitt Romney is Mormon should not have mattered either. Just because he's Mormon doesn't make me worry that he's going to make everyone wear those weird underwear. Nor am I worried that Barack has a pro smoking agenda, Hillary had a pro-woman agenda, or that McCain has a pro retiree agenda. It just wouldn't make sense for a candidate to do that.
What does matter is stated policies, candidate believability, and past track record. It's silly to focus on the little differences when there are much more important things we should be talking about.