Transparent Navigation Bars on 4.4

I am running Nova Launcher and enjoying the option to transparent nav bars on the top and bottom of my N4. Some questions i had if someone could clarify:

- When I used the default Kitkat launcher, the transparent navigation bars went away. So is this an N5 feature only for 4.4 stock launcher?

- It just feels weird when as soon as you open an app, the transparent navigation bars go away and are replaced by black bars. Has Google actually opened the navigation bar transparency option to allow app developers to take advantage of, like the Gallery and Play Book apps?