I think your authors are correct when you take the states as a whole, but when you break down the 2004 results by county and take a look at the county demographics, you see a wide dichotomy in voting patterns. Of course, many people voted against Kerry by voting for Bush, a huge mistake that's not reflected in the data on
this web site
This map uses a color scale that ranges from red for 70% Republican or more, to blue for 70% Democrat or more. This is sort of practical, since there aren't many counties outside that range anyway, but to some extent it also obscures the true balance of red and blue.
I trust you'll find this interesting.