Example of null ptr not = 0 ?

[DXB132 at psuvm.psu.edu]

I just read through the first section of the regular posting (common questions
and answers) (it's about 'null pointers') and I have a down-to-earth question:

Does there exist a C compiler for any "modern", commercial, 32-bit
(or more :-)) machine (i.e. a machine like you and I use) that uses something
other than zero (real binary zero) to mean "null pointer"? Why not just say in
the spec "a null pointer is zero!" and be done with the whole matter?
It just seems like a trivial academic exercise to talk about it any other way.
(My humble opinion, of course :-))

Apologies if this question irritates anyone.

-- Dan Babcock