Good analysis. But you overlook one critical variable.
The length of the Democratic nomination process forced the Republican attack machine to hold fire until it had a clear target. And the vigor with which Senator Clinton attacked Senator Obama's weaknesses meant that by the time the right got a hold of them, they would be old news.
So the fact that Obama is escaping the worst that the Republican dirty tricks squad can offer is, to a significant degree, a result of his battle with Senator Clinton. President Obama will owe Senator Clinton--big time!