I think what matters is what your primary account address is (I have more than 5 different shipping addresses in USA&Europe registered with Amazon, including my home address in EU). I've associated my 1-click address with one of the USA addresses I'm using, but I don't know whether this counts. I poked around My account section, but didn't find anything else to define my USA "residence" that allows me to get tons of free books.
When my primary address was in Europe, I got quite poor selection.
The 1-click doesn't mean I cannot ship to another address of course as you know, I just have to be careful where I'm sending it
