A hardware reboot is a must. Every phone without a removable battery simply has to have one; otherwise a reboot for non-responsive device would mean leaving it on until battery is drained and then recharging it back.
You just gave me nostalgia... I miss my old Blackberry
Sure, but hardware reboot can be a button in the paperclip slot, not the main power button.
Except then you're screwed if your phone bricks while you're out somewhere without a paperclip or similar implement. Holding down the power button for X seconds seems a far simpler and more user friendly solution. (Although I'm obviously in the camp that has never had my power button held down by something in my pocket for 10 seconds. Tough to imagine that happening.)
That's yet another reason why every phone should have a removable battery.