The traditional media thinks that Americans' primary voting criteria is how mediocre a candidate is, where more mediocre is more betterer. Guys who read and know stuff aren't like you and me - we want a lazy moron as president because he won't make us feel bad about ourselves. We can point to him and say "hey, I'm just as smart as that guy" or "hey, I could be doing a better job" and be right.
Along those lines: "Too Fit to Be President?" - Facing an Overweight Electorate, Barack Obama Might Find Low Body Fat a Drawback.