That makes the Android update policy look even more ridiculous. The iPhone 3GS came out June 2009, so with iOS 6 this phone will see update support for at least 4 years. My parents both got a HTC Desire which came out in Europe in March 2010 and are stuck at Android 2.3 with no chance of updating (4.0 is the newest version, with 5.0 coming later this year).
None of my friends ever sold his/her iPhone, they always gave it to other friends, which will probably use them until they break - also because the iPhones stay fresh with yearly iOS updates. Android phones seem to be designed to be outdated after just 12-18 months.