Why on god's green earth would you store something valuable on something that would take one random bonehead move for you to lose it?
Because an iPhone is like a laptop. Personal information that I may need while I am out and about I want with me. I have seen/heard of people misplacing/losing laptops and phones. People that are so absent minded should probably not have personal info on their phones but I always keep my phone in my pants pocket and don't misplace or lose my phone.