Apple has very different warranty policy for iPhone / iPad compare to Mac and iPod, this is due to the law and different network standard based on the country.
If you would like get your iPhone fixed in China, in or out of warranty at the Apple Store, you should buy from China or HK. HK is a tax free island, so its is the most popular destination place for electronic shopping.
The main reason Apple do this is to make sure All customers who bought the local version will being taken care of, in the meantime, to ensure the tax income to the Greater China, as HK is part of China, even with 2 policy and law, but Apple China (only Apple Store) still recognise the warranty validation of iDevices from HK.
To tell the iDevices is from HK or not, you can tell from the package tag, the model number ending with ZP, which means this is design for HK market. Chinese version ends with CH.
For more country model:
LL = USA
C = Canada
X = Australia
ZA = Singapore
B = UK
DN = Germany
KH = Korean