The idea is for a more consistent feel. No matter which way you hold the phone they will always be in the same place.
I think a big issue with it is the colour of the bar. Razr i has a much more attractive semi transparent bar.
It would be nice to adjust the transparency of the bar. That may come in a custom rom. Even so in use of the on screen buttons for a month now you do not miss the little space at the bottom of screen. Also from having the physical buttons the One S and X which could blaze away regardless the on screen buttons are a step in the right direction. I don't think there's any going back to physical buttons now anyway?
Nexus asked me elsewhere would I consider a Nexus 4? Got to say I'm not keen on the glass back. I carry my phone glass towards my leg for protection having broken a screen carrying phone with screen out in pocket. Glass back looks way to fragile for me. Kevlar backs all the way for me