Why is ident_is_sufficient different on Windows?

Hi there,

while trying to understand which parts of the author & committer identity are mandatory (name, email, or both), I ended up in ident.c, looking at ident_is_sufficient(), and to my surprise discovered that this seems to differ between Windows (were both are mandatory) and everyone else:

static int ident_is_sufficient(int user_ident_explicitly_given)
{
#ifndef WINDOWS
	return (user_ident_explicitly_given & IDENT_MAIL_GIVEN);
#else
	return (user_ident_explicitly_given == IDENT_ALL_GIVEN);
#endif
}

According to git blame, this was introduced here:

commit 5aeb3a3a838b2cb03d250f3376cf9c41f4d4608e
Author: Junio C Hamano <gitster@pobox.com>
Date:   Sun Jan 17 13:54:28 2010 -0800

    user_ident_sufficiently_given(): refactor the logic to be usable from elsewhere

The commit message sounds as if this was only a refactoring, but the patch to me look as if it changes behaviour, too. Of course this could very well be false, say due to code elsewhere that already caused Windows to behave differently; I wouldn't know.

Still, I wonder: Why does this difference exist?

Cheers, Max