I may be completely misinterpreting things, but it seems to me that the point is simply that the peg alone cannot be the biggest issue in the discussion.
David is correct. When discussing our current account deficit, the biggest issue is our low national savings rate, which is partly being driven by our fiscal recklessness. If Matthew Slaughter had written the beggar-thy-neighbor policies of the Chinese Central Bank were a small part of the story, he would have been correct. Our problem is that his WSJ oped suggested that these policies had no effect.