In general, people don't optimize their website for non-USA traffic. It never crosses many people's mind. Why would it? Who else would be looking for your site, anyway?I find it a bit surprising there are still people who don't optimize with internationalization in mind. Unless you offer a very narrow and local content or service, I think international visitors should always be granted with respect. If you don't want or can't support international visitors (because of commercial or logistic constraints), that's fine, but let them know as soon as possible!
Here in Quebec we are very sensitive and accustomed to this reality: we speak french while being surrounded by english culture. How many times to we end up on sites offering a french version assuming we are in France? How many times do we end up on a site to be abruptly abandoned after many promising steps to finally reach the lethal questions: state and zip code. Sorry "canadian", your "persona non grata".
Just for the sake of discussion, while the blog where this post came from shows 70% traffic from the US, my blog, with similar interests, shows radically different geographic spread:
All things being equal, notions like "foreign" and "overseas" don't make much sense anymore... we're all a bit "foreign" and, well, we're certainly all "overseas" somehow!