Ah yes you are right, an interesting point however,

    6.3.2.3 Pointers
    
       3. An integer constant expression with the value 0, or such an expression cast to type void *,
          is called a null pointer constant. If a null pointer constant is converted to a pointer type,
          the resulting pointer, called a null pointer, is guaranteed to compare unequal to a pointer
          to any object or function.
    
       4. Conversion of a null pointer to another pointer type yields a null pointer of that type.
          Any two null pointers shall compare equal. 

Looking at the definition of NULL:

    7.17 Common definitions <stddef.h>
    
        3 The macros are
        
                NULL
       
          which expands to an implementation-defined null pointer constant;

Meaning that NULL is implementation defined, but is assured by the standard to compare equal to any 0-valued pointer of any type, even if it is itself another special value.