Ta-da-m! This is the first question any usability/UI/whatever designer should ask: "Can software do this for users automatically?". Only then the designer should think of the visual appearence and interaction.

Doesn't work if you're traveling abroad. I hate getting country-specific versions of a site even after logging in with my US credentials. It should remember that I'm from the US.

You're presenting two different problems really.

1. Yes, sites should remember your personal preferences that you've already set.

2. When setting those preferences, pre-filling based on ip would work in 99.9% of locations. A standard selector can handle everyone else.