why warn for lack of AM_GNU_GETTEXT_VERSION?

[Ben Pfaff]

The gettext manual says this about AM_GNU_GETTEXT_VERSION:

       The use of this macro is optional; only the `autopoint'
    program makes use of it (*note CVS Issues::).

However, the autoreconf program will warn if
AM_GNU_GETTEXT_VERSION is omitted (if AM_GNU_GETTEXT is used).
Is it really optional or not, and if so then why warn about its
lack?
-- 
"A computer is a state machine.
 Threads are for people who cant [sic] program state machines."
--Alan Cox