or you can just borrow your friends?
Let me try to explain this better:
You have an iPhone 5. Your friend has iPhone 4S. You want to charge your iPhone, but didn't bring your charger.  Not a problem, because Apple uses a universal charger, right? You're screwed. Isn't it supposed to be "easier"?
And because it was such a hassle to use the same charger, Apple didn't throw in the adapter bit. So now, if you really need it, you can buy it from your local Apple Store for around 30$.