Not that risky, that was the first part of the article. Buying governmental debt is low risk, with the stats backing that up.
On your exchange rate comment; as long as our dollar is being devalued, investing in a foreign govt. debt, with it's own money (not being devalued by it's govt) you get the added bump in "value" of an exchange rate change bettering their (value)dollar against the USDollar.
Until the Fed / Obama/ Congress stops printing money to pay for it's bills, this will continue.