Ada.Command_Line.Argument_Count question

The RM has this to say about Argument_Count:

"If the external execution environment supports passing arguments to a 
program, then Argument_Count returns the number of arguments passed to 
the program invoking the function. Otherwise it returns 0. The meaning 
of �number of arguments� is implementation defined."

I'm wondering what that last sentence mean? Is the RM trying to tell me 
that Argument_Count cannot be trusted to yield the same result on 
different systems (Unix, BSD, Windows, Linux and so on)?

Or am I missing the point?

-- 
Regards,
Thomas L�cke

Email: tl at ada-dk.org
Web: http:ada-dk.org
IRC nick: ThomasLocke