I'm no Nate Silver, but it doesn't seem easy to dismiss two polls in the past three days showing Obama with just a four-point lead in Pennsylvania (even if one of them is the work of the GOP-friendly Rasmussen).
Bear in mind, though, that Obama can easily win the election without carrying Pennsylvania. Indeed, McCain could also carry Ohio and Florida and still come up short--so long as Obama carries the western swing states (Nevada, Colorado, New Mexico) plus Iowa and Virginia. He doesn't even need North Carolina here to reach a 270-268 win.
The response to this might be that if Obama loses OH PA and FL then something has gone terribly wrong in the home stretch and he can't expect to win those other states. Perhaps, but remember that McCain has targeted quite a lot of time and money on PA specifically, making it reasonable that it would break from the national norm.
Another response: That scenario would be an incredible letdown for Democrats looking for a mandate and to remake the electoral map.
Regardless, the fact remains that Pennsylvania is just not a make-or-break state. Which may explain why Obama has no plans to return there.