Let me break the election down for you into a tail of two coin flips.
To win the election, Romney needs to win both Virginia and Ohio.
Virginia - one coin flip = 50%
Ohio - a second coin flip = 50%
Getting heads in two coin flips = 50% x 50% = 25%
Unless the ground game shifts the numbers significantly, Romney has about a 25% of winning the election.
As far as the polling numbers go, it's as simple as that.