Right now, I can see Hash#identical and Hash#identical? in CVS HEAD.
However, in the Changelog we have:

Tue Sep 12 21:24:54 2006  Yukihiro Matsumoto  <matz / ruby-lang.org>

        * hash.c (rb_hash_compare_by_identity): rename Hash#identical to
          Hash#compare_by_identity.

Looking into this some more, it seems that it was originally #identical:
http://www.ruby-lang.org/cgi-bin/cvsweb.cgi/ruby/hash.c.diff?r1=1.167;r2=1.168
It was renamed to #compare_by_identity shortly after the initial patch
http://www.ruby-lang.org/cgi-bin/cvsweb.cgi/ruby/hash.c.diff?r1=1.168;r2=1.169
but the latter was reverted a couple days later
http://www.ruby-lang.org/cgi-bin/cvsweb.cgi/ruby/hash.c.diff?r1=1.169;r2=1.170
and the code has remained that way since then.

The ChangeLog entry and the CVS history (as well as the fact that
#compare_by_identity seems better than #identical) make me think that the last
modification was unintended.

-- 
Mauricio Fernandez  -   http://eigenclass.org   -  singular Ruby