Unfortunately it appears that USPS can not follow iso standards so many of the country names in l10n will not match for international shipping with usps.
I have a patch for a workaround but the patch only contains the mapping for Great Britain. The idea here is to map the three letter iso3code that the user chose as their country with the appropriate usps country name and use that. If it doesn't find a match then it will try to use the printable name. There are probably many others that don't match, perhaps as people find them they can fill in the dict until usps gets their act together.
Reported by jmather