Because, Paul, there is a hoofing great piece of channel behind there. If you look at the build, you'll see that this bit in the last pics is just the over-bumper. The fancy bit. Behind that is the actual winch bumper. It fits flush up to the outer part so that when it get hit, there's no room for deflection. All the wheel carrier assembly hangs off that too. It's a bumper of two halves in fact! It'll be fine. I intend to run a piece of strip under it too.
Chris