That is what Eve Fairbanks has pointed out. I'm inclined to agree - and it's also a sign that perhaps approval/disapproval is not the end-all and be-all of this election. There is a segment of those who disapprove of Bush from the right.
Back in 1972, Richard Nixon had an approval rating in the pits. He also won in a landslide despite an approval rating arguably worse than President Bush's. You see, while only 35% approved of his policy in Vietnam, a fair chunk of those who disapproved of hsi performance did so because they felt that Nixon wasn't fighing hard enough.
The same is true here. Bush takes criticism from those right who think he is not fighting hard enough, or doesn't declare Islam the enemy (as opposed to terrorists), or because he's not banning abortion immediately, or because he supports a comprehensive immigration reform bill. But will those disagreements result in votes for Democrats who favor outright anmesty and cutting and running in the war on terror?
Somehow, that's a stretch.