Thomas Borchert wrote:
The advantage to the "true" US certificate is that you can build
ratings

ok, may be this one changed, but I was able at the time to
add the US Instrument Rating on my private certificate based
on a foreign license.


the US certificate based on it would become invalid, too. One very
important possibility for that scenario lies in the extremely strict
medical requirements for private pilots in some European countries,
e.g. Germany. It's quite easy for a pilot to have his German medical
declined on a condition that would be perfectly ok in the US. Allowable
uncorrected vision, for example, is limited in Germany, it isn't in the
US.

indeed. but some foreign licenses were valid -- as far as 61.75 was
concerned -- indefinitely, regardless of you having the corresponding
foreign medical (and/or maintained the foreign currency
requirements); that was the case with the old British PPL(A).

--Sylvain