McCain has to hold other battlegrounds, VA, FL, IN and MO and get PA to get to 270.
PA would give him well above 270!
That's not entirely true. He would have to hold on to the ones you mentioned and PA only if Obama picked off other states. If he wins OH, FL, IN, MO, and picked up PA, then a VA or CO is not necessary. A switch for PA puts McCain in a good position, because he can then lose a couple red states from 2004. If he picked up the red states from last time, but lost CO, he can still win with a flip of NH or one other smaller state even w/o PA. A PA switch would be huge for McCain and probably puts him in the driver's seat. If PA stays blue, then McCain has to be almost error free and win back every Bush red state.