When I received my iPhone 3G last week, I was asked to register it. Not a necessary step for using the device, I know and easily skipped.
However, I was intrigued to find that even though I entered my Dutch address etc and specific 'Netherlands' in the country field, the next screen indicated that I was located in the 'United Kingdom'. The process thereupon asked me to re-enter my postal code, because it did not conform to the country. Logical, because the form factor of a Dutch postal code is different from a UK one.
I should perhaps mention that my input language is set as English (UK), although I cannot see that having anything to do with the matter. Moreover, the same happened when I wanted to register a Time Capsule some months back.