Interesting. I've found it to be just the opposite. I've had more resistance to Amex here in the states. Recent visits to SiN, UK, Spain, AMS, PRG, Peru, Brazil, etc. have found very few places that do not take Amex (and thse usually didn't take any cards). Definitely wider acceptance abroad, IME. Also, Citi CCs charge the highest rate I know (3%) for foreign transactions. By comparison, Starwood Amex is 2%.
Cheers.
I should have been more clear, "overseas" is a big place. I have found there are some countries where Amex is rarely taken outside of chain hotels and central shopping districts, etc. I noticed it most recently in France, at just about every restaurant or bar I went to that wasn't in Paris. Similar experiences in Thailand and Mexico, and almost no Amex accepted in Vietnam, for example. OTOH, I found Amex accepted everywhere in the UK. Etc. YMMV and all that.
Maybe it was just the French annoying me on purpose, again.