hum...wut? Battery life better on the iPhone? Compared to what? I have a Nokia 1100 at work that it's battery lasts for 5 days; compared to other smartphones is equal or worse (source: all my clients who haves iPhones, varying from the 4 to 5).
And how you easily get 3 days with casual use (i imagine email, websites browsing, sms, calls, etc.) is beyond my head.
I think he meant compared to other smartphones. I had a dumbphone (feature phone) that went a week with my normal usage, which on a dumbphone is really limited to calls and texts. Sure you can play games, surf the web, email on dumbphones, but it's not the same as a smartphone.
In any case, yeah, it's hard to imagine any modern smartphone getting 3 days of usage on Email, surfing the net, playing games, I have a HTC One, remember quad core CPU, massive 4.7" screen compared to iPhone, and I can easily go on 2 days of battery with about 5 hours of on screen time.
Having a closed ecosystem is a good thing in regards to battery life. With only one device to support, you better hope Apple gets the iPhone's battery life perfect.