Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Simple, you don't buy it off of EBay. That warranty is also with the "company" that is selling it to you, not Apple. My guess is that it is probably a knockoff but if it works, who cares.
 
knockoff chargers are about 1/2 of the weight of the standard REAL apple charger. cables sometimes have a longer plastic sheeting by the actual connector ends.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.