Spooky, the very reg you site says, "(2) After that, to fly for a period of 10 percent of the total time required to fly from the airport of departure .to, and land at, the airport to which it was released;"
Flag ops are international operations. Many of the rules go back to old Pan Am recip days. The rule for recip and turboprop operations require 15% of the enroute fuel. Sixty years ago weather guessing wasn't near what it is today. The extra fuel is to account for differences between the forecast winds and reality. Redispatch allows you to reduce the enroute time that you multiply by 10%.