I am glad I am not the only one wondering about this...
I have a roku connected to a large computer monitor mounted on the wall. Since it's a monitor, there is no remote and it's not convenient to reach for the power button. I used to never turn it off - it would just go to sleep when whatever I connected to it turned off.
Now, the backlight never goes off, since the roku is always sending a signal.
This seems like a no brainer feature. One of the "screen saver" option should actual allow to simply stop the video out, and let the monitor/tv sleep as well.