Both of you just summed up the problem of HDMI CEC. It is a standard, however no manufacturer implements it in accordance to the standard 100%. LG wants its TVs to work with LG HDMI devices over CEC, just like Samsung focuses on its own devices. They don’t care for others, they don’t care whether it works with their own devices in a year from now.
Probably LG has some custom code to turn off their TV from their BluRay player (etc.) or maybe they just thought it was a bad idea to let a connected device turn off the TV in the first place and never implemented it.