Software Buttons - that's why!
I've always been a fan of software buttons since the Galaxy Nexus was announced. Now many people disagreed with me saying that they take screen space away and so on... In my opinion they are the only smart choice in the current android world because many apps don't yet support the actionbar so you still need a fall back menu button. But for new apps no menu button is needed thus making it unesseccary.
But now Android 4.1 introduces Google Now which can be activated via a swipe up from the software home button - which is great in my opinion. You can activate it from anywhere very fast. You can't have this flexibility with hardware buttons. And this is just the beginning - google can add many more of these gestures in the next versions and you can only benefit from them if your phone has software buttons.
So I really hope more manufactureres see the benefits of software buttons vs hardware buttons (like Motorola).