I think this is what Ed Rollins was trying to say tactfully on the Lou Dobbs show. He said to ignore national polls and focus on states. Lou was adamant that we should pay attention to national polls but Ed stuck by his statement.
I think national polls are useful for gauging the trend. But, I agree with Ed: the individual state polls are far more important at this time. However, it's expensive to conduct a statistically significant poll in 57 states.
At some point, a national poll will reflect the states -- i.e. it's currently impossible to have a 10 point gap in a properly-conducted national poll without causing a large swing in electoral votes. If the country continues to become more polarized, that might no longer be true... but we aren't there yet.