Two years ago today, Standard & Poor's downgraded the credit rating of the United States, from AAA to a mere AA+. It was a psychological gut-punch, coming on the heels of a divisive standoff over raising the federal debt ceiling in which some Republican members of Congress threatened to allow the nation to tumble into default.

It also looks, with the benefit of hindsight, like the wrong call. Yes, the U.S. government might be dysfunctional. But over the past two years, prices in bond markets look like a wholesale rejection of the S&P thesis.

You would expect that if U.S. government debt was truly more risky than that of AAA rated nations, that the treasury would have to pay higher interest rates. But the verdict of the market these last two years cuts in the opposite direction. This chart shows the interest rate the U.S. government must pay to borrow money (the white line), along with AAA-rated Canada (the yellow line) and Australia (the green line). All three rates are indexed such that their 10-year rate as of Aug. 1, 2011, just before the debt downgrade, equals 100.

As the chart shows, rates have risen and fallen in concert over the past two years. But if any definable pattern is evident, it is that the AAA nations of Canada and Australia have had to pay a premium to borrow money compared with the AA+ rated United States. It is a sign that markets have never come around to the S&P view that the United states is in fact less creditworthy than Canada and Australia.

The pattern has only fallen apart in the past couple of months, as Australia's borrowing costs have fallen relative to those in the U.S. and Canada. That is the result more of the weakening of the Australian economy, closely tied as it is to a slowing China, than any shift in the perceived creditworthiness of the three nations.

Whatever you think of Standard & Poor's logic in concluding that poor U.S. governance makes its credit riskier, what is evident is that, two years on, markets aren't persuaded.