VP Location for the Democrats

Today's post will examine, from an election math perspective, what region Obama's running mate should be selected from (will examine the Republicans tomorrow). In the recent election past, the democrats have selected running mates from areas in which either they have no chance of winning or from very safe states. For example, in 2004, John Kerry selected John Edwards from North Carolina (which Edwards was unable to deliver to the democrats) and in 2000 Al Gore selected Joe Liberman from CT (which was very safe for Kerry). My question is why the democrats insist on picking VP candidates from the Northeast or traditional south. In examining the current polling data it seems that the logical choice for Obama is a running mate from either a key swing state (FL, PA, OH) or the Midwest/Southwest. While clearly there are many other factors that go into selecting a running mate, in terms of ticket balance and my opinion, selecting a candidate from the Northeast or the South would be a large mistake.