“unbound method”的含义在Python2和Python3中是否已经改变

Question

以下是通过inspect库获取类内方法的两端代码：
Python2

>>> class A(object):
...     def a(self):
...         print('a')
...     @staticmethod
...     def b():
...         print('b')
...     @classmethod
...     def c(cls):
...         print('c')
...
>>> import inspect
>>> inspect.getmembers(A, inspect.ismethod)
[('a', <unbound method A.a>), ('c', <bound method type.c of <class '__main__.A'>>)]

Python3

>>> class A(object):
...     def a(self):
...         print('a')
...     @staticmethod
...     def b():
...         print('b')
...     @classmethod
...     def c(cls):
...         print('c')
...
>>> import inspect
>>> inspect.getmembers(A, inspect.ismethod)
[('c', <bound method A.c of <class '__main__.A'>>)]

可以看到对于类而言，实例方法（unbound method)在Python3中已经不再是method，而是function.

>>> inspect.getmembers(A, inspect.isfunction)
[('a', <function A.a at 0x10d46e598>), ('b', <function A.b at 0x10d46e620>)]

通过查阅两个版本的inspect文档可以看到在Python2中：

inspect.ismethod(object)

Return true if the object is a bound or unbound method written in Python.

相对于在Python3中：

inspect.ismethod(object)
Return true if the object is a bound method written in Python.

ismethod不在包含unbound method了。

这是否是Python2到Python3后的通识区别？可惜这么重要的区别并没有被大多数的 “Differences between Python2 and Python3” 之类的文章提到。