Can rule C.128 be applied to C.129?

I have some questions about C.129 in connection with C1.128

C.129: When designing a class hierarchy, distinguish between implementation inheritance and interface inheritance

class Shape {   // pure interface
public:
    virtual Point center() const = 0;
    virtual Color color() const = 0;

    virtual void rotate(int) = 0;
    virtual void move(Point p) = 0;

    virtual void redraw() = 0;

    // ...
};

class Impl::Shape : public Shape { // implementation
public:
    // constructors, destructor
    // ...
    virtual Point center() const { /* ... */ }
    virtual Color color() const { /* ... */ }

    virtual void rotate(int) { /* ... */ }
    virtual void move(Point p) { /* ... */ }

    virtual void redraw() { /* ... */ }

    // ...
};

Why does Impl::Shape declare the member function inherited from the base class Shape as virtual?

From C.128 I expected that they should be override.

class Impl::Circle : public Circle, public Impl::Shape {   // implementation
public:
    // constructors, destructor

    int radius() { /* ... */ }
    // ...
};

Is there a technical reason why Impl::Circle::radios() is not declared override?

Can someone please help me to figure this out.