No current Roku responds to power command, the power keys on Roku remotes are strictly for Tv's.
Then why does my Roku turn off?
Some recent Rokus have the option to go into a low power state after a period of inactivity (about 20 minutes I think.) You can turn that off in settings if you don’t like it.
There have been a few times when I was trying the ways suggested in this thread to turn off the remote's ability to turn on and off the TV (it really shouldn't be that hard!) that I've pressed the button to turn things back on, and the TV comes on and indicates it isn't getting a signal from Roku. I have to manually turn Roku back on. It was off again this morning. When I get home I'll check the possibility you pointed out.
