If they’re admitting to 4pts > Bush , then Baraq must actually be about 5 pts below Bush at Bush’s worst. Don’t forget this was Bush after 8 years, Hussein hasn’t even gotten through his first (and hopefully last) term.
By 2007 anyone who had a GOOD thought about Bush was afraid to express it. Now many who have a BAD thought about Obama are afraid to express it. That would account for Obama doing slightly better than Bush in the poll. I think you are on the money.