Why does Osama want Bush to win?

Because once a terrorist is disconnected from any nation's support, Bush loses interest in catching that terrorist. Of course, terrorists can operate perfectly well without national support, so this policy is disastrous. Want an example other than Osama? Look at Zarqawi.

(Note: this is not the only reason. Osama also likes the way that Bush wanders into ambushes, alienates allies, unites Muslims against America, and gives Al-Qaeda a perfect recruiting tool.)