Watch the movie about Carl ROve and you'll get all your answers.
What got Bush elected a second time was above all else mobilizing the Conservative religious right. And personally I still have one of those fun little pamplets about how DnD is Satan worship and the like. It is an old thought, but one some people still have. So on one side he is associating Obama with DnD not ot get those people to not vote for Obama, but to get them to actively vote against Obama. Since they can't let someone who plays the "Satanic DnD" into the White House. Plus DnD still carries the Stigma of being a geeks game with some people, so then take the ones who don't want to be associated with that and at the very least swing them away from Obama if thye can't swing them to Mcain.
As petty and trival as it sounds those are the only voters they really have left, the middle voters who are not politically involved. So a sound tactic is to attack the petty little issues someone might have with a canidate or who else supports them, since to support the same person means you have something in common with everyone else who is supporting them. It's a movie, but look at Chris Rock's movie head of state. Imagine if someone actually got the public support of the KKK instead of it being a cheeky commerical. They might as well pull out of the presidental race, it would be the kiss of death. Since it is highly unlikely he can count on the KKK backing Obama, he has to go with something more obscure but in the back of the minds of some of the middle voters.