inheriting new and delete

I got this code from a friend of mine.

#include <iostream>

using namespace std;

class Base
{
   int i;
 public:
   Base(int ii=0):i(ii){}
   void * operator new(size_t sz)
   {
      cout<<"new sz="<<sz<<endl;
      return ::operator new(sz);
   }
   void operator delete(void* v,size_t sz)
   {
      cout<<"delete sz="<<sz<<endl;
      ::operator delete(v);
   }
};

class Derived:public Base
{
  int j;
public:
  Derived(int ii=0,int jj = 0):Base(ii),j(jj){}
};

int main(int argc, char *argv[])
{
  Derived *d = new Derived;
  delete d;
  Base *b = new Base;
  delete b;
  return 0;
}

I have a question here. operator new and delete functions are by
definition static to a class. So, if I have defined my own version of
operator new() or operator delete() in a base class, a derived class
should not inherit that from the base. But in the above code, for both
Base and Derived, the overloaded functions are being called. Can
someone please explain why ?

Thanks in advance.