I don't know how accurate this is, but I was considering purchasing Applecare from Ebay (US) as there's some great deals going on there. I rang Applecare UK and explained where I was looking to buy it from. The rep went away and checked and then explained that because the MacBook Pro is a portable product, it's covered worldwide but because the Applecare was purchased in the US, I would need to register it to an address in the US but Applecare would honour it here in the UK.
I'm not sure if this is correct as I don't know if Apple can tell if a particular agreement number was destined for a specific country, but I'd advise you ring and check yourself just in case.
It could have been that they just weren't sure and gave me that advice to keep themselves right.