I think because of the way import works, that a reload wouldn't update anything that the module you're reloading imports.

  $echo -e "def foo():\n\tprint 'bar'" > a.py
  $echo -e "import a\ndef bar():\n\ta.foo()" > b.py
  $python
  Python 2.5.2 (r252:60911, Jul 31 2008, 17:28:52) 
  >>>import b
  >>>b.bar()
  bar
  >>>f = open('a.py', 'w')
  >>>f.write("def foo():\n\tprint 'changed'")
  >>>f.close()
  >>>reload(b)
  <module 'b' from 'b.pyc'>
  >>> # Notice that it imported from 'b.pyc' not 'b.py'
  ... b.bar()
  bar
  >>>reload(a)
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
  NameError: name 'a' is not defined
  >>>#But I need to update a
  ...reload(b.a)
  <module 'a' from 'a.py'>
  >>>#That loaded from 'a.py'
  ...b.bar()
  changed
  >>>exit()

edit

  #You could have done it like this too
  >>>import a
  >>>import b
  >>>b.bar()
  bar
  >>>###Something changes a.py 
  >>>reload(a)
  >>>b.bar()
  changed