LG was one of the first to add the feature back around 2013. Now it's more commonly known as dt2w (double-tap to wake) and is a feature on a lot of stock roms, as well as pretty much any custom rom.

I believe it is, it's just never activated. My guess is they are saving that for a later upgrade when they can't add more cameras. I loved my LG with knock on, would still use it if it could handle today's apps...