My mistake, you are right.  I forgot about one of the many types that
CPython uses internally for built-in methods.  Indeed:

    >>> [].index == [].index
    False
    >>> [].__add__ == [].__add__
    True

I can fix this so that the answer is True in all cases; alternatively,
considering Frank Niessink's original issue, we could bring this
discussion to python-dev and decide what the correct behavior should be
and implement it consistently for all method types.