I think more phones are adopting the back power button. More stylish feel. I think the Japanese phones are the first to come out with back power button if I am not mistaken. Correct me if I'm wrong. Can't remember the brand, only recalled that the word docomo printed as I first came across that a few years ago when my friend showed me his jap smartphone which has fingerprint unlocking feature too. He told me it's intuitive that the index finger will always find the right spot when u hold the phone single-handedly. Moreover, it is waterproof and I got really impressed because there is no such smartphones with such capabilities at that time.