Why my Iphone5 could not repair in China?

My friend bought one iphone 5 for me from TaiWan on Jan,2013, due to the poor quality, the home button I found it does not work. So today I contacted the Apple retail store in ShenZhen(0755-26393400 Exit 5) and China Apple sevice No.400-627-2273 want them to give me more help for my Iphone, but I just be told by them that my iphone could not repair in China, they are only responsible for repairing the apple's product from Chain mainland, HongKong and Macao. TaiWan's products they could not repair. 😠 Why?????? I don't understand what reason they couldn't offer the sevice for me? Who can give me a reasonable explaintion??