Good question.
Obama just doesn't portray himself as any type of business/finance person. He looks like someone who was groomed to be a career public person. They really don't do anything except talk about what other people actually make and do.
Nothing with Obama defines him as a person of doing.
McCain had a life before politics and then a few side ventures like Keating, marrying money, etc.
Without a doubt Paulson could bs Obama, I suspect McCain would be a hard sell.