I've had the Motorola Atrix, Samsung GS3 and now the Nexus 4. The soft keys located at the bottom stay on... except when I am watching Hulu or Netflix. That's normal.
Over on the motorola.com forums, the official response is that they are working on it. I'm frankly astonished ... this was a problem on my OG Droid, Droid X, and now still years later it hasn't been fixed?