Why are the markets so optimistic about the US?

For the first time ever, investors are demanding a smaller premium to own U.S. corporate bonds than global company debt.

• In 2008, companies issuing debt in the U.S. paid 653 basis points more than Treasuries while corporations selling around the world paid 503 basis points more than sovereign governments offered investors in their debentures.
• But now, Bondholders demanded 166 basis points more in yield to hold U.S. investment-grade company debt instead of Treasuries at the end of 2010, compared with an average 169 basis-point spread worldwide

I suspect that the spreads say less about the differences between U.S. and foreign PRIVATE debt and more about the differences between US and foreign PUBLIC debt.