I said created, not maintained, if you read the book you will see later generations were later rewritten in C.
Of course you have to write on top of C, because that is what, sadly most operating systems are still written today.
But even that is slowly changing, when we look at the way operating system development is evolving, with safe layers on mini kernels, like Google is doing with Android or Microsoft with WP/WindowsRT/Singularity.
Anyway, I am stopping here, as won't convince you of anything and you won't convince me.
Most of other examples are about a thin layer of Pascal on top of (unsafe and non kosher) C.