Well, this started as "Why Joe Biden?"

The answer to that is simple and obvious. Sen. Biden is a mainstay in the Democratic Party (36 years as a senator from Delaware) and provides two key qualities: 1) he is believed to be able to draw the blue-collar rust-belt vote away from Sen. McCain, and 2) is ready to accept VP as his "swan song" from a Delaware elective office, making way for his son, the current Attorney General of Delaware to seek and hopefully easily acquire the "family" senatorial seat.

Sen. Biden has as much of a role and a kinship to Sen. Obama's camp as Sen. Johnson did in Sen. (later President) Kennedy's. Biden, like Johnson, is considered a "political necessity" during the campaign - an that's the end of the line for him after that.

For the voters, politics can be a clash of ideals and opinions. For the professional politicians, it is a business, and business partnerships and mergers occur only for the classical business reasons: 1) get rid of a competitor; and 2) make profit (votes). Just look at the "business" of both campaigns without idealistic rose-colored glasses - it's not pretty and sure isn't idealistic.

I'm not excluding the Republican Party from applying business tactics to politics. Both sides follow these "rules," hoping the customer (voter) is too dumb or blind to notice.