Yes, but which agency determines the rate of inflation? :)
At the end of the day, politicians could mandate that the government statisticians lie about the inflation rate (make it artificially low to lower CPI-index bonds payout rate).
But the currency markets would not be so easily fooled.
edit: Now that I think about, it isn't. They have inflation-indexed bonds as well. The more they print money, they bigger their debt grows!
http://www.treasurydirect.gov/indiv/products/prod_tips_glanc...