> "iterable" is described as "A container object 
> capable of returning its members one at a time."

That wording is confusing.  I'll fix it.

> Likewise, "and objects of any classes you define 
> with an __iter__() or __getitem__() method." is 
> wrong because __getitem__ method is not relate to
> iterable

That wording is correct.  Sequences are automatically
iterable even if they don't define __iter__.  For example:

>>> class A:
...     def __getitem__(self, i):
...         if i > 10:
...             raise IndexError(i)
...         return i * 100
	
>>> list(A())
[0, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000]

If you're curious, the details are in the PyObject_GetIter() function in http://svn.python.org/view/python/branches/release27-maint/Objects/abstract.c?view=markup .