What's going on here?

[Dale Strickland-Clark]

Python 2.4.2 (#1, Oct 13 2006, 17:11:24)
[GCC 4.1.0 (SUSE Linux)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> a = object()
>>> a
<object object at 0xb7bbd438>
>>> a.spam = 1
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
AttributeError: 'object' object has no attribute 'spam'
>>> class b(object):
...    pass
...
>>> a = b()
>>> a
<__main__.b object at 0xb7b4dcac>
>>> a.spam = 1
>>>

What is subclassing adding to the class here? Why can't I assign to
attributes of an instance of object?
-- 
Dale Strickland-Clark
Riverhall Systems - www.riverhall.co.uk