2 reasons: 1) Removing the battery on any electronic device is a foolproof way to shut it off. You don’t have to wait it to ‘power down’, and the reset buttons that many electronics have that you push with a safety pin often don’t work if the electronic is too screwed up. Removing the battery on a phone is the same as pulling the plug on your computer – you don’t have to wait for it to unfreeze to tell it to shut down or hope that the power button works. 2) iPhones (and iPods) don’t have very long lasting batteries. They tend to last no more than 2 years, which insures that people will spend lots of money replacing the battery, or just buying a new iPhone. As they are quite expensive to begin with, this can be frustrating since other phones batteries can last 5 years or more (and a replacement costs 20 dollars instead of 50–100 and can be bought at an electronics store instead of having to ship the whole phone in to Apple for them to replace for you) and many people find this process and huge expenditure to be a real problem.