They're not. But Linux supports a POSIX interface which is the basis of their compatibility.
I want to program using Linux without using libraries/wraps, etc.
That sounds painful.
so what is under ncurses when it comes to linux?
ncurses is a text based library. It allows you to writte anywhere in a text console and has higher level notions like Window and so on.
Can i do everything in curses, only using the kernel?
Curses has nothing to do with the Linux kernel. You're confusing the kernel with the user-land environment. If you want to play around with the kernel, you can do that, but that has little to do with writing a user application.
for example GTK+ & QT are built on top of Xlib(regarded as linux native gui api).
the linux kernel was used to build xlib?