I don't see how McCain won the "suburban" vote in PA, unless most of the area of the counties that surround Philadelphia are being classified as urban rather than suburban, while most of the area of the counties surrounding Allegheny are being classified as suburban rather than rural.
Likewise Nevada, unless all of Las Vegas and Reno are considered "urban".
CNN's exit poll classifications of that kind of thing have always been a little whacky. Like Alaska was collapsed as entirely Suburban and Rural in '04, not at all Small City/Small Town/whatever.
I think we put way more trust in exit polls than is warranted, even with our skepticism.