Well, the shell's chmod doesn't return an error.

[rgheck@rghstudy scripts]$ chmod 600 /media/IHP-100/Test.lyx
[rgheck@rghstudy scripts]$ echo $?
0
[rgheck@rghstudy scripts]$ chmod 400 /media/IHP-100/Test.lyx
[rgheck@rghstudy scripts]$ echo $?
0
[rgheck@rghstudy scripts]$ chmod 700 /media/IHP-100/Test.lyx
[rgheck@rghstudy scripts]$ echo $?
0
[rgheck@rghstudy scripts]$ python
Python 2.4.4 (#1, Oct 23 2006, 13:58:00)
[GCC 4.1.1 20061011 (Red Hat 4.1.1-30)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.chmod("/media/IHP-100/Test.lyx", 400)
>>> os.chmod("/media/IHP-100/Test.lyx", 600)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
OSError: [Errno 1] Operation not permitted: '/media/IHP-100/Test.lyx'

I don't know what would happen in C, say.