EMS (Which is Global Express, and says so on the
label) is trackable depending on the country that
is recieving it.  It tracks when it hits the PO,
when it gets a flight out, when it hits and clears
customs on the other end.  After that, it's
totally up to the recieving country.  USPS is
trackable down to "out for delivery" for the US.

Global Priority AFAIK is _NOT_ trackable outside
of the US.

It's not feasible for the USPS to deliver
everything in every country, which is what would
be required.  But for UPS and fedex, that's possible.