Why can @decorator not decorate a staticmethod or a classmethod?

Why can decorator not decorate a staticmethod or a classmethod in Python 2.6?

from decorator import decorator

@decorator
def print_function_name(function, *args):
    print '%s was called.' % function.func_name
    return function(*args)

class My_class(object):
    @print_function_name
    @classmethod
    def get_dir(cls):
        return dir(cls)

    @print_function_name
    @staticmethod
    def get_a():
        return 'a'

Both get_dir and get_a result in AttributeError: <'classmethod' or 'staticmethod'>, object has no attribute '__name__'.

Why does decorator rely on the attribute __name__ instead of the attribute func_name? (Afaik all functions, including classmethods and staticmethods, have the func_name attribute.)

It works when @classmethod and @staticmethod are the top-most decorators:

from decorator import decorator

@decorator
def print_function_name(function, *args):
    print '%s was called.' % function.func_name
    return function(*args)

class My_class(object):
    @classmethod
    @print_function_name
    def get_dir(cls):
        return dir(cls)
    @staticmethod
    @print_function_name
    def get_a():
        return 'a'