Actually, Apple warranty has limitation. China is one of the country where there are special requirement and warranty is only valid in that country. Let me do some research on my Apple internal site and get back to you on that.
Only in the US, Apple offers AppleCare Plus, which covers one time accidental coverage with $50 deductible+1 year of AppleCare. In my opinion, it's a good deal as Apple will simply replace the unit with a refurb unit and not repair it. Therefore there should be no issues of waiting for parts. I would rather buy the iPhone at full price in US so I get Canadian warranty.
Unless the phone has AWS 700/2100 reception (none that I know of in HK), then you can join Wind or Mobilicity with your own phone. T-Mobile's phone in US is also capable to use with Wind/Mobilicity.
EDIT: The warranty that is in China and Korea is called Variable Warranty. Since I cannot copy and paste the info, I attached the screeenshot for your reference: