I will also add that many (most?) US banks will not provide banking services for you if they know you live overseas. You have to maintain a US address. Even then, if they discover that despite having a US mailing address you actually reside overseas they will close your account. It's happening more frequently these days.
Wow, you're right! I looked into that just now. I figured USAA, which provides banking service to military and ex-military, and therefore likely has many members who live overseas, would be more likely to provide banking services to overseas Americans.
