The US income tax base excludes:(1) interest on state and local bonds, (2) employer contributions to pension and medical plans, (3) gifts and inheritances.

(by comparison, America's net foreign liabilities are 17% of GDP.) Much of their debt is being financed by local bank borrowing or bonds sold to investors in creditor countries, such as Germany.

HFT firms which seek to exploit currency movements or arbitrage price differences between local-currency and foreign-currency bonds want to move funds in and out of a country with minimal friction.