Obama's support: Miles Wide, Inches Deep

According to this story in the DMN, most Obama supporters didn't continue down the ballot. What might this mean if he does get the Democratic nomination? Would it make for better chances for our down-ballot candidates? Would it not matter?

I tend to think it would make for a better chance for Republican down-ballot candidates. If Obama's supporters check only his name, then they are not likely to check the straight-party vote, and they aren't likely to continue down the rest of the ballot either.