Agreed on that point. Nate Silver missed the Wyoming race, too, and he is not looking good on the North Dakota prediction. 55-45 is a big imbalance to overcome for control of the chamber. Even if Republicans can win the Senate race in every "Red State" in 2014, it only gets them to 50-50. It would take a very good day for Republicans on November 4, 2014, to give them the Senate for Obama's last 2 years.
Was thinking along the same lines. Getting up to 55 ensures continued control even if the GOP picks up all the possibilities next election. An unreported but important consideration, although a lot also depends on who gets primaried next time around.