VS11 is steady_clock, steady?

I just noticed the following code in <chrono.h>, which doesn't make sense to me.

struct system_clock
{
    static const bool is_monotonic = false; // retained
    static const bool is_steady = false;
};

class steady_clock
    : public system_clock
    {   // wraps monotonic clock
public:
    static const bool is_monotonic = true;  // retained
    static const bool is_steady = true;
    };

typedef steady_clock monotonic_clock;   // retained
typedef system_clock high_resolution_clock;

How can steady_clock be steady when it simply derives from system_clock which is not steady?